National Aeronautics and Space Administration

www.nasa.gov

Strange New Worlds
 
 

 

CONTENTS


About the Hubble Space Telescope 2


Introduction 4


CHAPTER 1: The Search for Other Earths 5


Probing the Atmospheres of Rocky, Habitable-Zone Planets 7


Spotting a World with a Glowing Water Atmosphere 9


Discovering an Alien Atmosphere that is Brimming with Water 10


Detecting Water Vapor on a Habitable-Zone Exoplanet 11


Exposing the First Evidence of a Possible Exomoon 13


CHAPTER 2: Weird Worlds 15


Capturing a Blistering Pitch-Black Planet 16


Finding a Shrinking Planet 17


Uncovering a Football-Shaped ‘Heavy Metal’ Exoplanet 19


Unraveling Mysteries Surrounding ‘Cotton Candy’ Planets 20


Tracking an Exiled Exoplanet’s Far-Flung Orbit 22


Revealing a Volcanic World that May Be on its Second Atmosphere 24


CHAPTER 3: Alien Weather 26


Using a Super-Jupiter’s Cloudy Skies to Measure its Rotation Rate 27


Forecasting Opposite Weather on ‘Cousin’ Hot Jupiters 29


Discovering a World that Snows Sunscreen 31


Unveiling a Planet with Yellow Skies 33


CHAPTER 4: Planet-Star Relationships 34


Pinpointing a Planet with Two Suns 35


Seeing a Star Sweep Helium from a Planet’s Bloated Atmosphere 36


Revealing that Small, Red Stars May Hinder Habitability 37


Exploring ‘Goldilocks’ Stars 39


CHAPTER 5: Disk Dwellers 40


Observing ‘Shadow Play’ Caused by Suspected Planet 41


Exposing an Otherworldly Case of Mistaken Identity 43


Gathering Evidence of a Planet Flinging Comets Into a Young Star 45


Puzzling Out the Atmosphere of a Mid-Size World 46


Measuring a Giant Planet’s Growth 47


SUMMARY 49


MORE INFORMATION 50


CREDITS 51


1 
About the Hubble Space Telescope
 

Since its launch in 1990, NASA’s Hubble Space Telescope has made more than one million observations, amassed 

a huge archive of scientifc fndings, and had a profound effect on all areas of astronomy Hubble has addressed 

fundamental cosmic questions and explored far beyond the most ambitious plans of its builders It has captured views 

farther out in space and further back in time than any other observatory to date Hubble has discovered that galaxies 

evolve from smaller structures, found that supermassive black holes are common at the centers of galaxies, verifed 

that the universe’s expansion is accelerating, probed the birthplaces of stars inside colorful nebulas, analyzed the 

atmospheres of extrasolar planets, and supported interplanetary missions The rate of discovery with Hubble is simply 

unparalleled for any telescope in the history of astronomy 

Hubble observes the universe from Earth orbit, just outside our planet’s atmosphere. 

Credit: NASA 

As NASA’s frst Great Observatory and the frst major optical telescope in space, Hubble ushered in a new era of 

precision astronomy The heart of the telescope is its 94 5-inch-diameter primary mirror It is so smooth that if it were 

scaled up to the width of the United States, there would be no bumps taller than six inches 

Operating above Earth, free from the blurring and fltering effects of our planet’s atmosphere, Hubble can resolve 

astronomical objects ten to twenty times better than typically possible with large ground-based telescopes It also can 

observe those objects across a range of the electromagnetic spectrum, from ultraviolet light through visible and to nearinfrared wavelengths 

Hubble can detect objects as faint as 31st magnitude, which is about 10 billion times fainter than the human eye can 

see The telescope can see faint objects near bright objects—an important requirement for studying the regions around 

stars and close to the glowing nuclei of active galaxies Astronomers have used Hubble’s sharp vision to probe the limits 

of the visible universe, uncovering never-before-seen objects that existed not long after the birth of the universe in the 

Big Bang 

Hubble’s view is optically stable, meaning the quality of its observing conditions never changes from day to day or even 

orbit to orbit Hubble can revisit celestial targets with the same acuity and image quality over and over again This is 

crucial for precision observations in which astronomers try to detect small changes in the light, motion, or other behavior 

of a celestial object 

2 
Hubble is more technologically advanced now than it was when launched, thanks to the maintenance and upgrades 

provided by fve space shuttle servicing missions between 1993 and 2009 Hubble is expected to continue operating 

for years to come 

Astronaut John Grunsfeld performs work on the Hubble Space Telescope during the frst of fve spacewalks conducted on the last servicing mission in 2009. 

Credit: NASA 

3 
INTRODUCTION 
 

This e-book is part of a series called Hubble Focus Each book presents some of Hubble’s more recent and important 

observations within a particular topic The subjects span from our nearby solar system out to the limit of Hubble’s view 

This book, Hubble Focus: Strange New Worlds, highlights some of Hubble’s recent discoveries about planets outside 

our solar system Hubble’s contributions are often in partnership with other space telescopes, as well as those on the 

ground, and build on decades of discoveries that came before Hubble’s launch Its fndings are helping us understand 

how our universe and our own planetary system have come to be the way they are today 

Ten “hot Jupiters” are on parade in this artist’s impression. One of several exoplanet categories, hot Jupiters are unlike any of the worlds in our solar system. They are 

enormous, like Jupiter, but orbit extremely close to their host stars. Studying hot Jupiters with Hubble helps astronomers learn more about how planetary systems form 

and evolve. 

Illustration credit: NASA and ESA 

4 
CHAPTER 1: The Search for Other Earths
 

For thousands of years, people believed that Earth was fxed at the center of the universe and that every other celestial 

object revolved around our planet But over time, it became clear that Earth did not occupy such a special position 

In 1610, Italian astronomer Galileo Galilei saw moons orbiting Jupiter in a series of monumental discoveries that 

strengthened an idea that had been around since at least the third century BC––heliocentricity This theory proposed 

that Earth and the other bodies in our solar system orbited the Sun As the previous framework for understanding the 

universe crumbled, people began to see that perhaps Earth was not as unique as they thought Some even wondered 

if there might be planets circling other stars 

Fast forward to today, and exoplanets––worlds beyond our solar system––are discovered in droves Astronomers 

have found more than 5,000 planets orbiting other stars The Hubble Space Telescope offers insight into what these 

worlds are like Most of the frst exoplanets astronomers unveiled were wild and exotic compared to the worlds in our 

solar system However, the prospect of fnding habitable, Earth-like planets that could host living things is also exciting 

Hubble has studied exoplanets’ atmospheres and found several that contain water vapor––an essential ingredient 

for life as we know it Some of these worlds even orbit within their star’s habitable zone, which is the range of orbital 

distances where temperatures are mild enough that liquid water could pool on planetary surfaces Hubble may have 

even extended Galileo’s discoveries of moons around Jupiter by potentially fnding a moon orbiting a planet located 

8,000 light-years from Earth The observatory will continue to help us learn more about exoplanets for years to come, 

offering clues about our own solar system’s formation and evolution along the way 

The planet visualized in this illustration, TRAPPIST-1f, is roughly the same size as Earth and orbits within its star’s habitable zone. Astronomers are interested in 

studying such worlds as part of the search for other Earths––other planets that could host life. 

Illustration credit: NASA/JPL-Caltech 

5 
Exoplanet names may seem complicated, but they have a logic behind them that is important to scientists cataloging thousands of planets. The frst part of the name 

is usually the telescope or survey that found the planet. For example, “WASP” stands for Wide Angle Search for Planets, “OGLE” is short for Optical Gravitational 

Lensing Experiment, and “Kepler” refers to the Kepler Space Telescope. “2M1207” is simply the name of 2M1307b’s host object, a brown dwarf. The lowercase letter 

“b” stands for the planet, in the order in which the planet was found. The frst planet found is named b, with ensuing planets named c, d, e, f, and so on. The star or 

other object that the exoplanet orbits is usually the undeclared “A” of the system, which can be useful if the system contains multiple stars, which themselves may be 

designated B, C. (Star designations are capital letters; planets’ are lowercase.) If several exoplanets around the same star are found at once, the planet closest to its 

star is named b with more distant planets named c, d, e, and so on. 

Illustration credit: NASA 

6 
Probing the Atmospheres of Rocky, Habitable-Zone 

Planets 

About 40 light-years away, seven Earth-size planets whirl around a diminutive “This discovery could be 

star in tiny orbits. Any of the planets in this system, called TRAPPIST-1, could 

a signifcant piece in the have liquid water depending on what their atmospheres are like. But the 

chances are highest for four that are located in the star’s habitable zone, puzzle of fnding habitable 

where conditions are neither too hot nor too cold for liquid water to pool 

environments, places that on planetary surfaces. The TRAPPIST-1 worlds were discovered by The 

Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile are conducive to life.” 

and the Spitzer Space Telescope, with assistance from several ground-based 

Associate Administrator, Thomas Zurbuchen, NASA telescopes. Hubble performed follow-up observations to probe several of the Science Mission Directorate 

system’s planets and help assess their habitability. 

First, Hubble observed the two innermost planets and found that they lack puffy, hydrogen-dominated atmospheres 

that are common for gaseous worlds like Neptune. Hydrogen is a greenhouse gas that can smother planets orbiting 

close to their host stars, making them hot and inhospitable to life. Astronomers think the two nearest TRAPPIST-1 

planets are likely rocky with atmospheres more similar to Earth’s, making it much more likely that the worlds could be 

habitable. The observatory then turned its sights on the four habitable-zone planets and discovered that at least three 

of them also lack hydrogen-rich atmospheres. Instead, their atmospheres may contain heavier gases like those found 

in Earth’s atmosphere, such as carbon dioxide, methane, and oxygen. 

NASA’s James Webb Space Telescope will observe the TRAPPIST-1 planets with even greater sensitivity, offering the 

opportunity to detect the chemical fngerprints of water, methane, oxygen, ozone, and other atmospheric components. 

Webb will also analyze the planets’ temperatures and surface pressures, offering vital information for assessing 

habitability. 

This artist’s concept shows what the TRAPPIST-1 planets may look like, based on available data about their diameters and masses. All seven of these worlds are about 

the same size as Earth, while the host star is barely larger than Jupiter (though more than 90 times as massive). Hubble studied several of the planets’ atmospheres 

and found that they could be conducive to life as we know it, though follow-up observations are needed to confrm this fnding. 

Illustration credit: NASA/JPL-Caltech 

Learn more: https://hubblesite.org/contents/news-releases/2018/news-2018-07.html 

7 
The TRAPPIST-1 planets, pictured in this illustration, all circle their host star much closer than Mercury orbits the Sun. In our solar system, such small orbits would 

render the worlds far too hot to be good candidates for life as we know it. However, since the host star is a red dwarf, which is much smaller and cooler than the Sun, 

its habitable zone is much closer in. Too close to the star, planets are too hot for liquid water, as indicated by steam in the graphic. Too far, and surface water exists 

only as ice, indicated by frost. Hubble observations showed that several of the planets, including three that orbit within the habitable zone, may be rocky and have 

atmospheres similar to Earth’s. 

Illustration credit: NASA and JPL/Caltech; Science: NASA, ESA, J. de Wit (MIT), H. Wakeford (University of Exeter/STScI), and N. Lewis (STScI) 

8 
Spotting a World with a Glowing Water Atmosphere 

Earth’s atmosphere has fve major tiers, including a stratosphere––home “We can now compare 

to Earth’s ozone layer, which protects us from the Sun’s harmful ultraviolet 

processes in exoplanet radiation Because of that UV radiation, the temperature increases with higher 

altitudes (unlike most atmospheric layers) Warm stratospheres are a common atmospheres with the 

component of the atmospheres in our solar system, though chemicals other 

same processes that than ozone, such as methane, are usually to blame However, scientists had 

never very confdently detected a stratosphere on an exoplanet until they happen under different 

trained Hubble on WASP-121b––a hot Jupiter located about 900 light-years 

sets of conditions in our from Earth 

own solar system ” 

While previous research revealed possible signs of stratospheres on some 

Mark Marley, NASA Ames Research Center other exoplanets, this new study presents the best evidence yet because 
 

scientists observed the signature of hot water molecules for the frst time 


Atmospheric water vapor behaves in predictable ways in response to certain wavelengths of light, depending on the 
 

temperature of the water If water molecules are cooler, they absorb certain wavelengths of light passing through them 
 

But if they’re warmer, they glow at the same wavelengths instead, which is what researchers saw on WASP-121b 
 

The team’s observations support theoretical models which suggest that stratospheres may defne a distinct class of 
 

ultra-hot planets Additional Hubble observations have explored WASP-121b’s stratosphere further, revealing iron and 
 

magnesium as the likely culprits behind the temperature increase in WASP-121b’s atmosphere 
 

The slightly egg-shaped exoplanet WASP-121b is seen near its host star in this artist’s impression. It orbits so close to its star that the top of its atmosphere is heated 

to a blazing 4,600 degrees Fahrenheit. By studying this planet’s atmosphere using Hubble, scientists detected the strongest evidence yet for a stratosphere––an 

atmospheric layer in which temperature increases with higher altitudes––on a planet outside our solar system. 

Illustration credit: NASA, ESA, and G. Bacon (STScI); Science: NASA, ESA, and T. Evans (University of Exeter) 

Learn more: https://hubblesite org/contents/news-releases/2017/news-2017-31 html 

9 
Discovering an Alien Atmosphere that is Brimming 

with Water 

Hubble teamed up with the Spitzer Space Telescope to study a hot, Saturn­ “WASP-39b shows us 

mass planet called WASP-39b, which is located about 700 light-years 

that planet formation is from Earth Astronomers dissected starlight fltering through the planet’s 

atmosphere and found clear evidence of a large amount of water vapor–– more complicated than 

much more than they anticipated, totaling three times as much water as 

we thought it was ” Saturn This was a surprising discovery because the planet orbits so close to 

its host star, completing one orbit in just four days If the planet formed in its Hannah Wakeford, Space Telescope Science Institute 

current, warmer location, its water would have evaporated into space and the University of Exeter 

WASP-39b is an excellent case study for planetary formation and evolution While Saturn likely formed near its present 

location, far from the Sun, astronomers think giant planets that orbit very close to their host stars likely formed farther 

away and then migrated inward over time WASP-39b observations strongly support this theory The planet probably 

accumulated its water much farther from its star, where cooler conditions allow icy material to exist and bombard the 

young planet Then WASP-39b likely made its epic journey inward, migrating to its current star-hugging location 

The James Webb Space Telescope could take an even more comprehensive look at WASP-39b’s atmospheric 

components, which are relatively easy to study because the planet’s atmosphere is not blocked by high-altitude clouds 

Webb may reveal information about this world’s atmospheric carbon, which absorbs light at longer wavelengths than 

Hubble can see By understanding the amount of carbon and oxygen in the atmosphere, scientists can learn even more 

about where and how this planet formed 

The hot, bloated planet WASP-39b hugs its star in this illustration. Hubble and Spitzer revealed that though WASP-39b is more than 20 times closer to its star than 

Earth is to the Sun, it contains a large amount of water in its atmosphere. This fnding strongly supports the theory that giant gas planets in tiny orbits likely formed 

farther from their host stars and then migrated inward over time. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2018/news-2018-09 html 

10 
 

Detecting Water Vapor on a Habitable-Zone Exoplanet for 

the First Time 

Astronomers have spent decades searching for other habitable worlds “This represents the 

Habitability for life as we know it is dependent on a non-poisonous atmosphere, 

biggest step yet taken a rocky surface, and a temperature range that allows water to pool on the 

surface Hubble detected water vapor in the atmosphere of a habitable-zone towards our ultimate goal 

planet for the frst time However, it fails to meet the other two habitability 

of fnding life on other criteria 

planets ” 

A team of researchers used data from Hubble’s archive to analyze the host 

Björn Benneke, University of Montréal star’s light fltered through K2-18b’s atmosphere They discovered signatures 

of water vapor as well as hydrogen and helium, the latter two of which are 

not hospitable for life as we know it With about eight times as much mass as Earth, K2-18b is probably a giant ball of 

gas and liquid like Neptune, with no rocky surface Its host star is also a very active red dwarf, which blasts high-energy 

radiation out into the planetary system 

But despite its hostile environment, K2-18b offered the frst opportunity for astronomers to detect and study water on a 

habitable-zone planet that likely features a temperate climate Future observations could estimate how much water the 

planet’s atmosphere contains, detect other molecules, and determine what percentage of the planet is cloud-covered 

K2-18b is especially interesting because it is one of hundreds of known super-Earths––planets with masses between 

those of Earth and Neptune The Transiting Exoplanet Survey Satellite (TESS) will likely discover hundreds more superEarths in the coming years, and the next generation of space telescopes will be able to take a more detailed look at their 

atmospheres As astronomers learn more about these fascinating worlds, we will come closer to fnding out whether 

Earth is unique 

Astronomers using Hubble data made the frst-ever detection of water vapor in the atmosphere of a planet that orbits within its star’s habitable zone. The system, 

shown in this illustration, is about 110 light-years away. It is home to a super-Earth called K2-18b, which is the only exoplanet known to have both water and 

temperatures that could support life. While astronomers are not sure whether K2-18b is truly habitable, studying it brings us closer to understanding whether other 

planets like Earth exist. 

Credit: ESA/Hubble, M. Kornmesser 

Learn more: https://hubblesite org/contents/news-releases/2019/news-2019-50 html 

11 
Hubble data revealed water vapor in a habitable-zone exoplanet’s atmosphere for the frst time. The planet, known as K2-18b, is a super-Earth, which may be the 

most common type of planet in our Milky Way galaxy. It also orbits the most common kind of star in our galaxy, called a red dwarf––a star that is much smaller, cooler, 

and more active than the Sun, which could affect the planet’s atmosphere and environment. Detecting water on a habitable zone exoplanet is a major step toward 

identifying other habitable worlds. 

Credit: NASA’s Goddard Space Flight Center 

12 
Exposing the First Evidence of a Possible Exomoon 
 

While astronomers have discovered more than 5,000 exoplanets so far, they “If confrmed, this fnding 

have yet to confrm the existence of an exomoon––a moon orbiting a world 

could completely shake beyond our solar system. However, using Hubble and the Kepler Space 

Telescope, researchers found evidence that a Neptune-sized moon may be up our understanding of 

circling the Jupiter-sized planet Kepler-1625b, located 8,000 light-years from 

how moons are formed Earth. While both the planet and possible exomoon orbit within their star’s 

habitable zone, they are both likely gaseous and therefore unsuitable for life and what they can be 

as we know it. 

made of.” 

If our solar system is a typical example, moons may drastically outnumber the Thomas Zurbuchen, NASA Headquarters 

planets in our galaxy. But since they tend to be much smaller than planets, 

they are more diffcult to detect. Researchers frst inferred the presence of 

a large moon orbiting Kepler-1625b by monitoring the light from its host star using Kepler. The planet transited, or 

crossed in front of, its host star, which temporarily dimmed the star’s light. But the dimming contained wobbles which 

could indicate that the planet is not alone––a giant moon, around four times larger than Earth, may whirl around it. 

Hubble observed the planet as a follow-up to the Kepler observations, also using the transit method. Researchers 

gathered a more detailed look at the dips of light, which included a secondary dimming that could be caused by a 

moon. Since the scheduled Hubble observations ended before the team could measure a complete transit of the 

candidate moon and confrm its existence, follow-up observations are necessary to validate the exomoon. The James 

Webb Space Telescope could fnd and study candidate exomoons in greater detail, possibly revealing very small ones. 

A large, gaseous moon lurks in the shadow of its parent planet in this illustration of the Kepler 1625 system. While the moon is enormous––roughly the same size as 

Neptune, or four times as large as Earth––astronomers estimate that it is only 1.5 percent as massive as the planet it orbits, which is several times more massive than 

Jupiter. This mass-ratio is similar to the one between Earth and our Moon, but fnding such a large moon may cause experts to revisit theories about how moons form 

around planets. 

Illustration credit: NASA, ESA, and L. Hustak (STScI) 

Learn more: https://hubblesite.org/contents/news-releases/2018/news-2018-45.html 

13 
This video visualizes Hubble data that indicates a moon may be orbiting the distant planet Kepler-1625b. Follow-up observations are necessary to confrm whether an 

exomoon is the defnitive cause of the anomalies researchers saw in the host star’s light as the planet crossed in front of the star. 

Credit: NASA’s Goddard Space Flight Center and J. Koynock 

14 
CHAPTER 2: Weird Worlds
 

When astronomers began hunting for planets orbiting other stars, they expected to fnd systems similar to ours Instead, 

they discovered swarms of strange and exotic worlds that required a reevaluation of planetary formation and evolution 

theories, which were developed to explain how our own solar system came to be Hubble’s exoplanet studies continue 

to help broaden our view of planetary systems by revealing even more oddballs, often by investigating the chemistry of 

their atmospheres via spectroscopy 

Hubble’s spectroscopic observations have unveiled withering worlds that dwindle as they lose their atmospheres to 

space, sometimes releasing a stream of heavy metals These leaky planets could help explain why astronomers fnd 

relatively few hot, Neptune-sized worlds––while many likely form, they may have a tendency to shrink The mission has 

also revealed a world that gobbles up nearly all of the starlight that reaches the planet, rather than refecting it back into 

space This strange planet would look as black as fresh asphalt if we could see it directly Another world Hubble studied 

is in such an extreme orbit that it’s on the verge of being ripped apart, as the host star’s gravitational pull stretches a 

once spherical world into a football shape Scientists using Hubble have even found evidence that a planet orbiting a 

distant star may have lost its atmosphere but gained a second one through volcanic activity 

Extreme worlds are often the easiest to discover because they have the strongest, most detectable effect on their host 

star But these planets are certainly not the easiest to understand Hubble, in tandem with other observatories, will 

continue to reveal new information about the worlds that grace our galaxy, helping unveil a more complete picture of 

planetary formation and evolution 

A “sub-Neptune” world withers under the fery radiation its young, hot host star is emitting in this illustration. Hubble results have shown that such active stars can 

bake away their planets’ atmospheres, leaving airless, rocky cores behind instead. But Hubble has also revealed that some of these wilted planets could generate allnew atmospheres. 

Credit: ESA 

15 
Capturing a Blistering Pitch-Black Planet 

About 1,400 light-years from Earth, an inky alien world dubbed WASP-12b “This research further 

circles a Sun-like star Far from resembling any of the planets in our solar 

demonstrates the vast system, WASP-12b––a member of a class of planets called hot Jupiters––is 

gargantuan and hellishly hot It hangs so close to its star that it spins only diversity among the 

once per orbit––a phenomenon called tidal locking The same side always 

faces its star, just like we always see the same side of the Moon, which is strange population of hot 

tidally locked to Earth This heats the atmosphere on WASP-12b’s day side to Jupiters ” 

a roiling 4,600 degrees Fahrenheit, so hot that water vapor molecules break 

Taylor Bell, McGill University and the Institute for apart Yet the planet’s night side is more than 2,000 degrees cooler, which is Research on Exoplanets mild enough for clouds to form 

Astronomers using Hubble found that although most hot Jupiters refect about 40 percent of the starlight falling on 

them, WASP-12b refects less than 10 percent The planet traps so much light that it would look as black as fresh 

asphalt if we could see it directly, hinting that refective aluminum oxide clouds are not present on the planet’s day side 

The researchers made this discovery by using Hubble to view the components of light (or spectra) given off by the 

system By observing how much the system dimmed as the planet passed behind the star, they could determine how 

much starlight the planet refects Their observations did not detect any dimming, which means the daytime side of the 

planet is absorbing nearly all of the starlight falling onto it This result draws a stark contrast to the only other hot Jupiter 

observed this way, hinting at the wide variety among these extreme worlds 

This illustration shows one of the darkest known exoplanets, called WASP-12b, orbiting extremely close to a star like our Sun. Hubble observations revealed that it 

gobbles up nearly all of the starlight that reaches the planet, rather than refecting it back into space. This light-eating prowess is due to the planet’s unique capability 

to trap at least 94% of visible starlight falling into its atmosphere. A swirl of material from the planet’s super-heated atmosphere is seen spilling onto its star in this 

illustration. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2017/news-2017-38 html 

16 
Finding a Shrinking Planet 

The exoplanet hunt has revealed a shortage of Neptune-sized worlds located “This is one of the most 

precariously close to their host stars These planets, dubbed “hot Neptunes,” 

may not have strong enough gravity to hold on to their atmospheres in the extreme examples of 

face of the powerful stellar radiation that comes from having such small a planet undergoing a 

orbits Astronomers discovered strong evidence in support of this theory 

when Hubble observations revealed that the planet GJ 3740b is rapidly losing major mass-loss over its 

mass as its atmosphere evaporates lifetime ” 

Prior to this discovery, only one similar planet (GJ 436b) was observed leaking Vincent Bourrier, University of Geneva 

its atmosphere into space Both planets are known as “warm” Neptunes 

because they orbit farther from their host stars and therefore are cooler 

than hot Neptunes The more recently studied planet is losing its atmosphere about 100 times faster than the frst 

Astronomers estimate that GJ 3740b has already lost more than a third of its original mass and may ultimately shrink 

down to the most common type of known exoplanet, a mini-Neptune The team detected the ultraviolet-light signature 

of hydrogen in a huge cocoon surrounding the planet as it passed in front of its star The cocoon is evidence of the 

planet’s atmosphere bleeding off into space If this phenomenon is widespread among exoplanets, it could explain the 

hot Neptune void––while many likely form, they may have a tendency to shrink Studying such worlds further will help 

us learn more about how planets form and evolve 

Astronomers expected to fnd many “hot Neptunes” orbiting very close to their stars, but so far the search has turned up relatively few. This plot, which looks like 

someone has taken a bite out of it, reveals the so-called hot Neptune desert. Hubble observations of the planet GJ 3740b support the theory that these worlds may 

shrink over time as their atmospheres evaporate into space. 

Credit: NASA, ESA, and A. Feild (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2018/news-2018-52 html 

17 
Astronomers used Hubble to detect a giant cloud of hydrogen streaming off the warm, Neptune-sized planet GJ 3740b, located just 97 light-years from Earth. The 

cloud, shown in blue in this artist’s illustration, is evidence that the planet is shrinking as its atmosphere escapes into space. The fndings lend credence to a theory 

that explains why so few Neptune-sized worlds are found orbiting extremely close to their host stars––while many probably form, they may dwindle over time as their 

atmospheres leak away. 

Credit: NASA, ESA, and D. Player (STScI) 

18 
Uncovering a Football-Shaped ‘Heavy Metal’ Exoplanet 

Astronomers used Hubble to observe WASP-121b and for the frst time “This planet is being 

detected the heavy metal gases iron and magnesium streaming away from 

actively stripped of its an exoplanet Iron and magnesium are known as heavy metals in astronomy 

because they are heavier than lightweight hydrogen and helium These atmosphere ” 

chemicals are thought to cause the increasing temperature in a layer of the 

David Sing, the Johns Hopkins University planet’s atmosphere, which astronomers previously detected using Hubble 

Scientists previously detected strong evidence of a stratosphere on WASP-121b, leading them to study it further The 

planet orbits so close to its star that the top of its atmosphere is heated to a sweltering 4,600 degrees Fahrenheit 

Hubble observations reveal that the lower atmosphere is also hot enough for iron and magnesium to be gaseous, 

allowing them to stream to the upper atmosphere where they escape into space on the coattails of hydrogen and 

helium The heavy metals can escape because while the planet is big, it is not dense, making its gravity relatively weak 

Researchers used Hubble’s unique sensitivity to ultraviolet light to search for the signatures of magnesium and iron 

imprinted on starlight fltering through WASP-121b’s atmosphere as the planet passed in front of its host star WASP121b will be an excellent target for the James Webb Space Telescope, which is optimized for the longer, infrared 

wavelengths that water and carbon dioxide are visible at The combination of Hubble and Webb observations would 

give astronomers a more complete inventory of the chemical elements that make up the planet’s atmosphere Further 

observations could also add to the developing story of how planets lose their primordial atmospheres 

This artistic illustration reveals how WASP-121b’s atmosphere is scorched and blown away by a torrent of ultraviolet light from its star. Hubble observations revealed 

that the star is super-heating the planet’s atmosphere, baking off heavy metals like iron and magnesium. WASP-121b orbits the star so closely that it is on the verge of 

being ripped apart. The powerful gravity of its nearby star has stretched the planet out, making it appear more oblong (like a football) than round. 

Credit: NASA, ESA, and J. Olmsted (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2019/news-2019-19 

19 
Unraveling Mysteries Surrounding ‘Cotton Candy’ Planets
 

The planets in our solar system are vastly different from each other––just “This system offers a 

compare the small, rocky planet Mercury to the bloated, gas giant Jupiter 

unique laboratory for But an even wider variety of worlds circle other stars Thanks to Hubble, we 

now know that our galaxy is even home to “cotton candy” planets testing theories of early 

planet evolution ” Rather than being made of spun sugar, Hubble observations confrmed 

that three super-puffy planets in the Kepler 51 system have extremely low Zach Berta-Thompson, University of Colorado Boulder 

densities Astronomers discovered the planets in 2012 using the Kepler 

Space Telescope and measured their densities two years later Combining 

Kepler’s data with the most recent Hubble results refned the mass and size estimates for these worlds The team found 

the planets’ masses by monitoring their orbital motion, and then combined that with the planets’ sizes to determine how 

dense they are Though they appear to be as big and bulky as Jupiter, they are actually one hundred times less massive 

The researchers used Hubble to investigate the chemistry of two of these strange planets’ atmospheres, searching 

for signs of water As each planet passes in front of the host star, starlight shines through the atmosphere allowing 

astronomers to detect its chemical makeup To their surprise, the search came up empty Obscuring clouds of particles 

high in the planets’ atmospheres are the likely culprits for the missing chemical signature Unlike Earth’s water-clouds, 

the clouds on these planets may be composed of salt crystals or photochemical hazes, like those found on Saturn’s 

largest moon, Titan The James Webb Space Telescope may be able to peer through the cloud layers, potentially 

providing insight into what these low-density, cotton-candy-like planets are actually made of 

This illustration shows three swollen planets in the Kepler 51 system, located about 2,600 light-years from Earth, orbiting their Sun-like star. These strange, puffy 

worlds have been dubbed “cotton candy planets” because they are Jupiter-sized but with much lower densities, based on Hubble observations. 

Credit: NASA, ESA, and L. Hustak, J. Olmsted, D. Player, and F. Summers (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2019/news-2019-60 

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Artist illustrations of the three bloated planets in the Kepler 51 system are compared to photos of worlds in our solar system to show their relative sizes. While the 

Kepler 51 planets are around Jupiter’s size, they are one hundred times less massive. Astronomers using Hubble confrmed their puffy nature, which may indicate that 

they formed farther from their star and then migrated inward. Now much closer to their host star, their low-density atmospheres will likely evaporate into space over 

the next few billion years. 

Credit: NASA, ESA, and L. Hustak, and J. Olmsted (STScI) 

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Tracking an Exiled Exoplanet’s Far-Flung Orbit
 

Nearly all of the currently known exoplanets orbit closer to their host stars than “It’s as if we have a time 

Earth orbits the Sun But Hubble has revealed that a giant world called HD machine for our own 106906 b circles its two host stars in a gigantic 15,000-year-long orbit Its path 

is very elongated and tilted with respect to the disk of debris encircling the host planetary system ” 

stars, hinting that the world’s current location may be a result of a game of 

Paul Kalas, University of California planetary pinball that transported it from a much closer original position 

Astronomers discovered HD 106906 b using the Magellan Telescopes in Chile, but learning about its orbit required 

something only Hubble could do: track the vagabond’s motion with extreme precision across more than a decade A 

team of researchers mined Hubble’s archive for this data, marking the frst time astronomers were able to measure the 

motion of a massive planet that is orbiting very far away from its host stars and visible debris disk The prevailing theory 

to explain the planet’s strange orbit is that it formed much closer to its host stars, but the drag from the system’s gas 

disk caused the planet’s orbit to decay, forcing it to migrate inward Then the host stars’ gravity nearly slingshot the 

planet out of the system, but a passing star stabilized the planet in a new, enormous orbit Astronomers have identifed 

candidate passing stars using the European Space Agency’s Gaia satellite 

The strange planetary system offers insight into what may have happened in our own solar system billions of years 

ago Circumstantial evidence suggests that a planet with fve times Earth’s mass, dubbed Planet Nine, may be lurking 

in the outskirts of our solar system beyond Pluto’s orbit Though the search for Planet Nine continues, HD 106906 b is 

evidence that such oddball orbits are possible 

About 336 light-years away, a planet called HD 106906 b––shown in this illustration––circles a pair of host stars in an unlikely orbit. Hubble revealed that the world 

orbits its stars at a distance of about 68 billion miles, more than 700 times farther than Earth is from the Sun. This observation could offer clues about a hypothesized 

distant member of our solar system, dubbed Planet Nine. The HD 106906 system is only 15 million years old, suggesting that our Planet Nine––if it does exist––could 

have formed very early on in the evolution of our 4.6-billion-year-old solar system. 

Credit: NASA, ESA, M. Kornmesser (ESA/Hubble) 

Learn more: https://hubblesite org/contents/news-releases/2020/news-2020-53 

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This video simulates a possible orbit for the vagabond planet HD 106906 b, showing its skewed, elongated path. Hubble masked light from the system’s central twin 

stars to reveal the surrounding debris disk, which is akin to our own Kuiper Belt, and the orbiting planet. HD 106906 b’s enormous orbit is evidence that other planets 

may occupy similarly large orbits, including the hypothesized Planet Nine in our own solar system. 

Credit: NASA, ESA, P. Kalas (University of California, Berkeley and SETI Institute), and J. DePasquale (STScI) 

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Revealing a Volcanic World that May Be on its Second 

Atmosphere 

Hubble’s vast data archive contains untold treasures waiting to be mined “We believe the 

One such treasure was uncovered by astronomers who were exploring small 

atmosphere that we see planets that have lost their atmospheres The rocky world GJ 1132 b, located 

just 41 light-years from Earth, stood out because its spectrum showed now was regenerated ” 

that it does have an atmosphere––a toxic haze of hydrogen, methane, and 

Raissa Estrela, NASA’s Jet Propulsion Lab hydrogen cyanide 

Its composition hints that it is not GJ 1132 b’s original atmosphere, which was likely blasted away by radiation from the 

planet’s host star Researchers think the planet’s new atmosphere is continuously replenished as molten lava oozes up 

through volcanic fssures Gas seeps through the cracks and into the sky in a process called outgassing, and eventually 

escapes to space Astronomers had never found a secondary atmosphere on an exoplanet before This discovery 

could indicate that similar worlds may have detectable atmospheres as well 

The key to GJ 1132 b’s atmosphere is volcanic activity, which scientists think occurs on this planet because it orbits so 

close to its star that it experiences extreme tidal heating This phenomenon is similar to Earth’s ocean tides, which rise 

and fall each day because of the Moon’s gravitational pull on Earth Since GJ 1132 b and its star are far more massive 

than the Moon and Earth, the effect is much more exaggerated All of the stretching and pulling the planet experiences 

as it orbits the star creates enormous amounts of friction, which heats the planet’s interior and makes volcanism and 

outgassing possible Jupiter’s volcanically active moon Io experiences the same phenomenon due to the giant planet’s 

gravity Future observations by the James Webb Space Telescope may allow scientists to see down to the planet’s 

surface The mission’s infrared vision could spot volcanic areas since they will be hotter than their surroundings 

This plot shows the model atmospheric spectrum (orange line) scientists made using data points from GJ 1132 b’s observed spectrum (blue dots with error bars). The 

planet wasn’t expected to have a detectable atmosphere, but its spectrum suggests that it consists primarily of hydrogen with notes of methane, hydrogen cyanide, 

and aerosols. Scientists think this analysis marks the frst discovery of an exoplanet’s secondary atmosphere, which was replenished after the planet lost its original 

atmosphere. 

Credit: NASA, ESA, Pam Jeffries (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2021/news-2021-013 

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Scientists using Hubble have found evidence that a planet orbiting a distant star may have lost its atmosphere but gained a second one through volcanic activity. The 

planet, GJ 1132 b, is hypothesized to have begun as a gaseous world with a thick hydrogen blanket of atmosphere. Starting out at several times the diameter of Earth, 

this so-called “sub-Neptune” is believed to have quickly lost its primordial hydrogen and helium atmosphere due to the intense radiation of the hot, young star it orbits. 

In a short period of time, such a planet would be stripped down to a bare core about the size of Earth. That’s when things got interesting. 

Credit: NASA Goddard Space Flight Center 

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CHAPTER 3: Alien Weather
 

Earth exhibits a wide range of weather, from rolling thunderstorms to sunny skies to blizzards Thanks to Hubble, 

astronomers have also monitored the weather on our neighboring worlds, revealing sulfuric acid rain on Venus, cloudy 

skies on Uranus, storms on Neptune, and more But Hubble’s exoplanet observations have unveiled even more exotic 

weather 

Astronomers used Hubble and the Magellan II Telescope to study WASP-79b, a hot Jupiter with a blazing atmosphere 

that is so hot that its scattered clouds might rain molten iron The researchers also found that the planet does not 

experience the same blue light scattering effect that we see on Earth Instead, they saw the opposite effect, which likely 

means the planet’s skies appear yellowish instead of blue In another study, Hubble revealed stark differences between 

two “cousin” hot Jupiters While the planets are similar in several respects, researchers were surprised to learn that 

one is very cloudy while the other has clear skies Perhaps most startling of all, Hubble has also revealed a world that 

snows sunscreen on the planet’s permanent nighttime side The discovery marked the frst time astronomers detected 

this precipitation process, called a cold trap, on an exoplanet 

Hubble’s exoplanet observations complement those of other telescopes, which sometimes follow up on its fndings to 

provide additional data Further studies will yield clues about how different planets form and what drives their weather 

activity 

Rain, snow, sunny skies––exoplanets can experience weather just like Earth does, sometimes with their own strange twists. Some planets, like WASP-43b, shown 

above, feature extreme temperatures and winds because they orbit so close to their host stars. Others are home to toxic rain and snow due in part to their bizarre 

atmospheres. Hubble continues to help us study alien weather to learn more about the worlds that populate our galaxy. 

Credit: NASA, ESA, and Z. Levay (STScI) 

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Using a Super-Jupiter’s Cloudy Skies to Measure its 

Rotation Rate 

Measuring the length of a day on our neighboring world Mars was relatively “This result gives us a 

simple Using a telescope, Dutch astronomer Christiaan Huygens spotted a 

unique technique to dark splotch on the red planet’s surface and tracked how much time it took 

for the feature to return to the same position Around 350 years later, a team explore the atmospheres 

of scientists used a similar method but a far more powerful instrument–– 

the Hubble Space Telescope––to make the frst direct measurement of an of exoplanets and

exoplanet’s rotation rate, thanks to its cloudy skies measure their rotation 

rates ” Astronomers previously used Hubble to observe the planet, dubbed 

2M1207b, and discovered that it rains glass high in the atmosphere and Daniel Apai, University of Arizona 

molten iron at lower altitudes The bizarre world is located about 170 lightyears from Earth and orbits a brown dwarf––a so-called failed star, which is 

not massive enough to power itself by nuclear fusion the way stars do Since the brown dwarf is so dim and far from 

the planet, astronomers more recently used Hubble to observe 2M1207b directly The planet is so young that it is still 

hot as it contracts under gravity, making it glow in infrared light Using Hubble’s infrared vision, astronomers saw that 

the planet rhythmically fickers as it spins on its axis like a top The subtle changes in the planet’s brightness are likely 

due to a variegated cloud cover of comparatively bright and dark patches 

Based on their observations, astronomers estimate the gaseous world completes one rotation approximately every 10 

hours, which happens to be nearly the same as Jupiter’s rotation rate The James Webb Space Telescope will help 

astronomers better determine 2M1207b’s atmospheric composition and derive detailed maps from brightness changes 

with the new technique demonstrated by Hubble’s observations 

This image shows the brown dwarf 2M1207A (left) and an orbiting planet, 2M1207b (right). Planets are usually diffcult to see directly because their host stars tend 

to be so bright that orbiting planets are lost in the glare. But 2M1207b glows brightly in infrared light since it is so young and hot while 2M1207A is quite dim since it 

doesn’t shine like stars do. Astronomers using Hubble blocked the brown dwarf’s light to see 2M1207b directly and measured fuctuations in the planet’s brightness. 

This suggests the planet has patchy clouds that appear to ficker as the planet spins. 

Credit: NASA, ESA, and Y. Zhou (University of Arizona) 

Learn more: https://hubblesite org/contents/news-releases/2016/news-2016-05 html 

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This artist’s illustration features the super-Jupiter planet 2M1207b in the foreground and its parent brown dwarf in the background. The planet orbits at a distance of 

about fve billion miles––nearly twice as far as Neptune is from the Sun. Because the planet is only 10 million years old, it is so hot it may rain molten glass and iron in 

its atmosphere. Hubble has measured fuctuations in the planet’s brightness that suggests the planet has patchy clouds as it completes one rotation every 10 hours. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

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Forecasting Opposite Weather on ‘Cousin’ Hot Jupiters
 

Most of the frst few hundred exoplanets astronomers discovered were hot “We don’t see what we’re 

Jupiters––wild worlds that are vastly different from those in our solar system 
 

Recent Hubble results show that there is great diversity among hot Jupiters; expecting with these 
 

while some have sunny skies, others are covered in thick blankets of clouds 
 planets, and we need to 

Researchers used Hubble to study two remarkably similar planets: WASP-67 understand why ” 

b and HAT-P-38 b While they are nearly the same temperature and size, and Giovanni Bruno, Space Telescope Science Institute 

orbit very similar host stars at the same distance, their atmospheres could 

hardly be more different The researchers used Hubble to search for spectral 

signs of water by analyzing how starlight fltered through the planets’ atmospheres Since WASP-67 b’s spectrum 

lacks water signatures, the team concluded that the planet is bland-looking with a high cloud deck But they did fnd 

spectral fngerprints of water in HAT-P-38 b’s atmosphere, indicating that the planet must have relatively clear skies, 

which allowed them to see deep into the atmosphere Since these “cousin” planets have such different atmospheres, 

scientists think something in their past must have infuenced the way they evolved Further research using Hubble and 

the James Webb Space Telescope could offer valuable clues 

This diagram compares Hubble observations of two strikingly similar exoplanets: HAT-P-38 b and WASP-67 b. For each of these worlds, astronomers measured 

how light from the host star flters through the planet’s atmosphere. WASP-67 b’s spectrum is relatively fat, lacking an absorption feature that indicates that water 

is present. This suggests that the atmosphere is masked by high-altitude clouds. HAT-P-38 b’s spectrum, however, bumps upward in the middle, which means the 

atmosphere contains water. Scientists interpret this peak as evidence that the upper atmosphere is free of clouds or hazes. 

Credit: Artwork: NASA, ESA, and Z. Levy (STScI); Science: NASA, ESA, and G. Bruno (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2017/news-2017-22 html 

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This illustration compares the atmospheres of two hot Jupiters. While they are too far away for Hubble to see their atmospheres directly, scientists can infer what 

they look like by studying the planets’ spectra. Since HAT-P-38 b’s spectrum shows the presence of water, it likely has relatively clear skies. However, WASP-67 b’s 

spectrum lacks the spectral signature of water, indicating that most of its atmosphere is masked by high-altitude clouds. Future observations could help explain why 

these planets have such different atmospheres. 

Illustration credit: NASA, ESA, and Z. Levy (STScI) 

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Discovering a World that Snows Sunscreen 

Precipitation is extremely common on our planet. But it isn’t unique to Earth; “These studies are 

some other worlds have their own exotic variations. For example, astronomers 

testbeds for how we’re using Hubble discovered that it snows titanium dioxide––a common ingredient 

in sunscreen––on the hot Jupiter called Kepler-13Ab––but only on one side going to do atmospheric 

of the planet. 

studies on terrestrial, 

Kepler-13Ab is tidally locked to its star, which means the same side of the Earth-like planets.” 

planet always faces the star while the other is trapped in an endless night. 

Thomas Beatty, Pennsylvania State University Astronomers used Hubble to study the planet’s atmosphere in near-infrared 

light as the world passed behind its star, an event called a secondary eclipse. 

Observing the secondary eclipse allowed astronomers to gather the temperature of atmospheric components on the 

planet’s day side. The researchers found the giant planet’s atmosphere is cooler at higher altitudes––the opposite of 

what they expected. 

Hot Jupiters typically have a gaseous form of titanium oxide that absorbs light and heats the upper atmosphere. 

Astronomers think high winds on Kepler-13Ab carry titanium oxide around to the permanently dark side of the planet, 

where it condenses to form clouds and falls as flurries of titanium dioxide. The planet’s gravity is so strong that the 

titanium dioxide can’t be recycled back into the upper atmosphere on the planet’s day side. Instead, it remains trapped 

on the night side, leading astronomers to call this precipitation process a “cold trap.” These Hubble observations 

marked the first time astronomers detected a cold trap on an exoplanet. 

Kepler-13Ab looms large among some of the planets in our solar system in this illustration. Known as a hot Jupiter due to its size and proximity to its star, Kepler-13Ab 

is one of the hottest known planets with a dayside temperature of nearly 5,000 degrees Fahrenheit. Astronomers used Hubble to study the planet’s atmosphere and 

found that it snows sunscreen (titanium dioxide). 

Illustration credit: NASA, ESA, and A. Feild (STScI) 

Learn more: https://hubblesite.org/contents/news-releases/2017/news-2017-36.html 

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This illustration shows the scorching hot planet Kepler-13Ab that orbits extremely close to its host star, Kepler-13A, which is part of a multiple star system. The star’s 

companions, Kepler-13B and the small orange dwarf Kepler-13C, are in the background. Astronomers used Hubble to study Kepler-13Ab’s atmosphere and for the 

frst time they detected a strange precipitation process called a cold trap on an exoplanet. This cold trap produces some wild, sunscreen-snowfall weather on the 

permanently dark side of the planet. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

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Unveiling a Planet with Yellow Skies 

Harnessing the power of multiple telescopes often enables astronomers to “This is a strong 

learn more than they could otherwise Hubble teamed up with the Magellan 

indication of an unknown Consortium’s Magellan II Telescope in Chile to study WASP-79b, a hot Jupiter 

located about 780 light-years away The planet’s atmosphere is about 3,000 atmospheric process that 

degrees Fahrenheit, which is so hot that its scattered manganese sulfde or 

we’re just not accounting silicate clouds might rain molten iron While that may seem startling, the real 

surprise for astronomers was that the planet’s sky isn’t blue for in our physical 

models ” Earth owes its azure skies to Rayleigh scattering, a phenomenon where very 

fne dust particles in the upper atmosphere disperse shorter, bluer wavelengths Kristin Showalter Sotzen, the Johns Hopkins University 

of light Astronomers combined Hubble and Magellan observations to fnd Applied Physics Laboratory 

that WASP-79b does not experience Rayleigh scattering Instead, they 

saw the opposite effect––shorter wavelengths of light appear to be more transparent Researchers are not sure what 

atmospheric processes may be causing it, but the result is that the planet’s skies likely appear yellowish instead of blue 

These fndings support independent observations by the Transiting Exoplanet Survey Satellite (TESS) 

The water vapor Hubble spotted in WASP-79b’s atmosphere designated it as a prime target for the James Webb Space 

Telescope Webb’s observations will provide a detailed view of the planet’s chemical makeup, which could yield clues 

about how its atmosphere has evolved and perhaps reveal the secret behind its amber skies 

The steamy world in this illustration, WASP-79b, orbits its host star in just 3.5 days. But its orbit brings the planet around the star’s poles instead of the equator, defying 

planetary formation theories. Astronomers used Hubble and the Magellan II Telescope to study the strange world and found even more surprises––its sky is likely 

yellowish instead of blue. 

Illustration credit: NASA, ESA, and L. Hustak (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2020/news-2020-18 

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CHAPTER 4: Planet-Star Relationships
 

To learn as much as we can about planets throughout our galaxy, astronomers must consider the relationship between 

these worlds and their host stars If our own host star, the Sun, were just a little hotter or colder, or if it were much older 

or younger, Earth might not be habitable Hubble has helped astronomers explore what other planetary systems are like, 

offering clues to how they may evolve and informing our search for habitable worlds 

Using Hubble, astronomers brought a little piece of science-fction to life by confrming that a world like Luke Skywalker’s 

home planet Tatooine––a world with two suns––actually exists The planet was discovered using a ground-based 

telescope, but astronomers needed Hubble’s crisp resolution to distinguish both of the small, faint host stars 

Hubble has also studied different types of stars to explore which are most conducive to life Astronomers used the 

telescope to study small, red stars and found that they are extremely violent when they are young Another study 

revealed that rocky worlds orbiting red dwarfs may be bone dry and lifeless Water and organic compounds, essential 

for life as we know it, may get blown away before they can reach the surface of young planets 

While Sun-like stars may be the most obvious targets to search for habitable planets, Hubble revealed that orange 

dwarfs––smaller and cooler than our yellow-white Sun, but larger and hotter than red dwarfs––could offer better 

chances These stars are not too hot, too cool, or too violent to host life-friendly planets over vast stretches of cosmic 

time Hubble’s future observations will continue to help us focus our search for habitable worlds, bringing us ever closer 

to the possibility of fnding life on other planets 

Stars and planets often have intricate relationships. The system shown here features a planet, called HD 189733b, that is tidally locked to its star––one side always 

faces the star, while the other is always dark. Hubble has revealed that stars can have even more extreme effects on orbiting worlds, sometimes blasting planetary 

atmospheres away and rendering entire worlds uninhabitable. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

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Pinpointing a Planet with Two Suns 

Astronomers using Hubble confrmed that a world like Luke Skywalker’s home “We needed Hubble’s 

planet Tatooine is located 8,000 light-years from Earth The planet, known 

crisp resolution to tease as OGLE-2007-BLG-349L(AB)c, orbits a pair of small, faint stars Scientists 

have known such worlds, called circumbinary planets, exist since the frst one out the identities of the 

was discovered in 2011 However, this was the frst to be confrmed using a 

members of this planetary quirk of gravity called microlensing 

system ” 

When two stars closely align from our vantage point, the gravity of the nearer 

David Bennett, NASA Goddard Space Flight Center star can bend, or “lens,” the light from the farther star Astronomers see this 

effect as a temporary increase in the distant star’s brightness Planets orbiting 

the nearer star can also create a detectable effect, changing the pattern of the lensed light The planet OGLE-2007­

BLG-349L(AB)c was originally detected by a collaboration of fve different observing teams using the microlensing 

method, but it was unclear whether the system contained one planet orbiting two stars or a pair of planets orbiting a 

single star The data revealed that the mass of the star or stars in the system totaled 70% of the Sun’s mass 

Ultra-sharp Hubble images settled the mystery, confrming that the Saturn-mass planet is circling two stars in a tight 

orbit around each other The diminutive stars are only 40% and 30% of the Sun’s mass, respectively Scientists came 

to this conclusion because a single star that is 70% of the Sun’s mass would be much brighter than two smaller stars, 

even if they add up to the same combined mass The system, collectively called OGLE-2007-BLG-349, aligned nearly 

perfectly with a background star, which allowed astronomers to determine such detailed properties 

This artist’s illustration shows the planetary system known as OGLE-2007-BLG-349. The identities of the members of this system were unclear from ground-based 

observations. Hubble’s high-resolution follow-up observations revealed that the system contains a gaseous, Saturn-mass planet orbiting two red dwarf stars. 

Illustration credit: NASA, ESA, and G. Bacon (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2016/news-2016-32 html 

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Seeing a Star Sweep Helium from a Planet’s Bloated 

Atmosphere 

About 200 light-years from Earth, a windy world called WASP-107b orbits “This new technique 

a turbulent star Scientists using Hubble observed the system and found may help us detect that the star is blasting helium out of the planet’s upper atmosphere This 

discovery marked the frst time astronomers detected helium in an exoplanet’s atmospheres around 

atmosphere Earth-sized exoplanets, 

Scientists originally thought helium would be one of the most readily- which is very diffcult with 

detectable gases on giant exoplanets, especially because it is the second- current technology ” most common element in the universe after hydrogen However, decades of 

searching exoplanets for the element came up empty It took Hubble’s infrared Jessica Spake, University of Exeter 

vision to spectroscopically tease out the element’s presence in WASP-107b’s 

atmosphere When the planet passed in front of its star, Hubble detected 

helium’s fngerprints in the starlight fltered through WASP-107b’s atmosphere Based on how much helium they found, 

astronomers think the planet’s atmosphere must stretch tens of thousands of miles into space The host star’s strong 

radiation and stellar winds are blasting the world’s atmospheric gases away at a signifcant rate, totaling between 1-4% 

of the atmosphere’s total mass every billion years As a result, the planet leaves a trail of material in its wake as it makes 

its six-day orbit around its star 

Astronomers had never discovered an exoplanet’s extended atmosphere using infrared spectroscopy before, relying 

instead on ultraviolet and optical wavelengths of light Using infrared vision extends such studies to a wider range of 

planets, including ones that orbit farther from their host stars Future telescopes, such as the James Webb Space 

Telescope, will use this new method to analyze exoplanet atmospheres in far greater detail than ever before 

The planet WASP-107b crosses in front of the face of its tempestuous host star in this artist’s illustration. The same size as Jupiter but only 12% of Jupiter’s mass, 

WASP-107b is one of the lowest density planets astronomers have discovered. Using infrared spectroscopy, scientists using Hubble found helium the host star is 

blasting out of the planet’s atmosphere. 

Credit: ESA/Hubble, NASA, and M. Kornmesser 

Learn more: https://hubblesite org/contents/news-releases/2018/news-2018-26 html 

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Revealing that Small, Red Stars May Hinder Habitability
 

Host stars strongly infuence the habitability of orbiting planets Two Hubble “These low-mass stars 

studies indicate that M dwarfs––small, red stars––are often poor hosts, are critically important in bathing their planets in harmful radiation and blasting away ingredients that 

are necessary for life as we know it These results have implications for the understanding planetary 

search for life throughout the galaxy atmospheres ” 

M dwarfs are very common and live extremely long lives, however a Hubble Evgenya Shkolnik, Arizona State University 

program found that these stars produce violent superfares when they are 

young The program, called Habitable Zones and M dwarf Activity across Time (HAZMAT), surveyed M dwarfs at three 

different ages: young, intermediate, and old The HAZMAT team found that ultraviolet fares from the youngest red 

dwarfs they surveyed, which are around 40 million years old, are 100 to 1,000 times more energetic than when the 

stars are older Such intense fares of high-energy radiation may blast the atmospheres away from fedgling planets–– 

especially terrestrial worlds, whose atmospheres change dramatically in the frst 100 million years 

Another study revealed more bad news for rocky worlds circling M dwarf stars While some orbit within their star’s habitable 

zone, where the temperature could allow liquid water to pool on the planets, they may be bone dry and lifeless instead 

Hubble and the European Southern Observatory’s Very Large Telescope in Chile discovered a rapidly eroding disk of gas and 

dust around the nearby M dwarf star AU Microscopii (AU Mic) Fast-moving blobs of material are excavating the disk, acting 

like a snowplow by pushing small particles––possibly containing materials like water––out of the system Astronomers are 

not sure how the blobs originated, though one theory proposes that the turbulent star’s powerful mass ejections expelled 

them This suggests that many rocky planets around M dwarf stars may not harbor water or organic material 

A fery M dwarf star is blasting a fedgling planet’s atmosphere away in this illustration. Powerful fares from young M dwarf stars may render orbiting planets 

uninhabitable, based on Hubble observations. As part of the same study, astronomers also detected one of the most intense stellar fares ever observed in ultraviolet 

light. 

Illustration credit: NASA, ESA, and D. Player (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2018/news-2018-46 html 

https://hubblesite org/contents/news-releases/2019/news-2019-02 html 

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These two Hubble images, taken six years apart, show a debris disk around the young M dwarf star Au Mic. Hubble’s coronagraph blocked out the glare from the star 

to view fainter features in the disk. An arrow traces the movement of a blob of material, which is zipping along at nearly 15,000 miles per hour. Astronomers were able 

to study this system in such detail partly because it’s so close to Earth––only 32 light-years away, while other M dwarf systems with starlight-scattering debris disks 

are typically about six times farther away. 

Credit: NASA, ESA, J. Wisniewski (University of Oklahoma), C. Grady (Eureka Scientifc), and G. Schneider (Steward Observatory) 

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Exploring ‘Goldilocks’ Stars 

While M dwarf stars may be poor hosts for planets, surveys by Hubble and “The Kepler-442 system is 

other telescopes have revealed that our galaxy is home to “Goldilocks stars ” 

Small, orange stars called K dwarfs are not too hot, too cold, or too violent to a Goldilocks planet hosted

host habitable planets over vast stretches of time by a Goldilocks star!” 

Edward Guinan, Villanova University As part of the “GoldiloKs” Project, scientists used Hubble, the Chandra 

X-ray Observatory, and the European Space Agency’s XMM-Newton satellite 

to probe relationships between a star’s age, rotation rate, X-ray and ultraviolet emissions, and fare activity Hubble 

performed sensitive ultraviolet observations to study radiation from about 20 K dwarf stars, while other telescopes 

focused on larger G stars, which are like our Sun Conventional wisdom suggests that Sun-like stars would be prime 

candidates to host life-bearing planets, however researchers found that K dwarfs may be more hospitable 

K dwarfs are a happy medium because they’re about three times as common as G stars and live much longer lives 

They are not as common or long-lived as M dwarfs, however they are much milder; while M dwarfs commonly produce 

potentially planet-sterilizing fares, K dwarfs lack the intensely active magnetic felds that generate such outbursts As a 

result, orbiting planets would only receive about 0 01 times as much deadly X-ray radiation as worlds orbiting M dwarfs 

K dwarfs also have mid-sized habitable zones, compared to M dwarfs (which have small habitable zones close in) and 

G stars (which have wider habitable zones farther out) Scientists also took a closer look at some of the K stars that host 

planets They found that the star Kepler-422 is home to a rocky planet that is about twice as massive as Earth Future 

observations could study this potentially habitable world’s atmosphere to search for possible signs of life 

This infographic compares the characteristics of the smallest three classes of stars in our galaxy: Sun-like G stars, cooler and less massive K dwarfs, and even cooler 

and smaller M dwarfs. M dwarfs are most common and live the longest lives, however they have small habitable zones and blast orbiting planets with X-ray radiation. 

G stars are much milder and have wide habitable zones, however they have much shorter lives and are less common. K dwarfs are in between, both in size and 

characteristics, making them the best candidates for potentially hosting habitable worlds for long periods of time. 

Credit: NASA, ESA, and Z. Levy (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2020/news-2020-06 

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CHAPTER 5: Disk Dwellers
 

New stars emerge into the Milky Way from swirling clouds of gas and dust that are peppered throughout our galaxy 

Vestiges of those clouds remain, surrounding each star in a disk that grows ever more diffuse as debris clumps together 

to form objects like planets Hubble’s exoplanet studies have largely focused on the worlds themselves, but occasionally 

surprises pop up in the disks these planets are embedded in 

For example, astronomers trained Hubble on a nearby star and saw an enormous shadow sweeping across its 

surrounding disk An unseen planet orbiting close to its star may be warping the inner part of the disk, blocking the 

star’s light and casting the looming shadow Hubble revealed A separate observation revealed an imposter exoplanet’s 

disappearing act, hinting that a full-grown planet never existed in the frst place Instead, Hubble may have captured the 

aftermath of a colossal collision between two icy bodies 

Hubble has helped study comets that a planet is hurling into its star, and probed a rare mid-size planet’s atmosphere 

The latter observation could help astronomers understand why so few planets between the sizes of Earth and Neptune 

exist––the disks they orbit in may dissipate before the worlds can bulk up further Using Hubble, astronomers have even 

studied a growing planet that is gobbling up material from the disk surrounding its host star 

By revealing new information about the dusty disks planets live in, Hubble helps astronomers learn how planetary 

systems form and evolve and offers additional insight into how our own solar system came to be 

This artist’s illustration shows two 125-mile-wide bodies colliding in orbit around the star Fomalhaut, located just 25 light-years from Earth. Astronomers using 

Hubble likely saw the aftermath of this collision, though it was frst identifed as a planet. Subsequent observations showed the object expanding and fading until it 

disappeared, supporting researchers’ recent conclusion that it was never a planet at all. The dust cloud from the collision has now ballooned to more than 200 million 

miles across, making it so diffuse that Hubble can no longer detect it. Smashups like this are estimated to happen around Fomalhaut once every 200,000 years. 

Hubble was looking at the right place at the right time to capture this rare event. 

Credit: ESA, NASA, and M. Kornmesser 

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Observing ‘Shadow Play’ Caused by Suspected Planet
 

Nearly all the information we receive from space comes in the form of light But “This shadow phenomenon 

shadows can be telling, too Astronomers using Hubble noticed a mysterious may be fairly common in dark splotch covering an enormous portion of a disk of dust and gas encircling 

a young, nearby star Since Hubble had observed the star, called TW Hydrae, young stellar systems ” 

multiple times over the previous 18 years, the team was able to assemble a 

John Debes, Space Telescope Science Institute time-lapse movie that revealed a strange phenomenon––a gigantic shadow 

whirling around the disk like the hands moving around a clock 

TW Hydrae’s 41-billion-mile-wide disk is tilted face-on to Earth, providing Hubble with a bird’s-eye view of the system 

When astronomers combed through Hubble’s image archive to investigate the strange shadow, they found that it 

sweeps around the disk in a regular motion, completing a lap every 16 years Scientists say the feature moves much too 

quickly to be physically part of the disk Instead, the shadow may be the result of an unseen planet that orbits too close 

to the star––around 100 million miles away, nearly as close as Earth orbits the Sun––for Hubble or any other presentday telescope to see it directly 

Astronomers think the possible planet may be pulling on nearby material and warping the inner part of the disk 

The misaligned portion of the disk blocks the star’s light, casting a large shadow on the outer disk Submillimeter 

observations by the Atacama Large Millimeter Array (ALMA) in Chile support this explanation, and even reveal a gap in 

the disk An unseen planet could create such a gap as it clears debris out of its path The new Hubble study offered a 

unique way to probe what is happening very close to the star 

About 190 light-years from Earth, an unseen world may be doing some heavy lifting. The theorized planet circles a star called TW Hydrae, which is only eight million 

years old. Astronomers think the planet is gravitationally pulling on material near the star and warping the inner part of the disk of gas and dust that surrounds it. A 

twisted, misaligned inner disk would explain the shadow Hubble spotted on the outer disk. 

Credit: NASA, ESA, and A. Feild (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2017/news-2017-03 html 

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Watching an Eerie Shadow Haunt a Young Star
 

This simulation shows a shadow moving around the disk of gas and dust that encircles the young star TW Hydrae. The video is based on Hubble data taken between 

1998 and 2016, and it also projects the shadow’s future motion around the disk. Astronomers think a planet is pulling on material near the star and warping the inner 

part of the disk, though the planet is too close to the star for Hubble to detect it directly. The misaligned inner disk is casting its shadow across the surface of the outer 

disk. The planet must be roughly Jupiter’s size to have enough gravity to pull material up out of the plane of the main disk. The planet’s gravitational pull causes the 

inner disk to wobble around the star, giving the shadow its 16-year rotational period. 

Credit: NASA, ESA, and J. Debes (STScI) 

42
Exposing an Otherworldly Case of Mistaken Identity 
 

In 2008, astronomers announced that Hubble captured its frst image of a “This is a blueprint of 

planet orbiting another star, called Fomalhaut, about 25 light-years from Earth 

how planets destroy each However, a team of researchers from the University of Arizona suggests that 

the object was actually a billowing cloud of dust, which would explain why it other ” 

seems to have disappeared 

George Rieke, University of Arizona Steward 

Observatory 

The “planet,” called Fomalhaut b, was puzzling in several ways Its orbit was 

strange, and it was unusually bright in visible light yet lacked detectable infrared 

heat signatures Then as astronomers performed follow-up observations during subsequent years, the object appeared to 

fade until it vanished entirely The University of Arizona team mined Hubble’s data archive to trace the object’s disappearing 

act, concluding that it was never a full-grown planet in the frst place 

Instead, the researchers think two icy bodies in the disk surrounding Fomalhaut collided and shattered, spilling dust into 

space in an expanding cloud Such collisions have happened in our own solar system billions of years ago, leaving behind 

rocky debris that we can still see today as asteroid families No one has ever seen one of these cataclysmic events around 

another star because they are so rare, occurring about once every 200,000 years in Fomalhaut’s case But Hubble’s 

original observations of the Fomalhaut system may have witnessed the aftermath, which appeared as a small dot next to a 

giant ring of icy debris encircling the star Follow-up observations using the James Webb Space Telescope will study more 

details of Fomalhaut’s debris ring and will look for evidence of other, bona fde planets in the system 

This diagram shows the fndings of several years of Hubble observations. It illustrates what astronomers consider evidence of the aftermath of a titanic collision in 

another star system. The Hubble image on the left is a vast ring of icy debris encircling the star Fomalhaut. A black disk blocks the star’s glare, so the dust ring is 

visible. The diagram on the right zooms in to trace Hubble’s observations of an object orbiting the star. While astronomers originally thought the object was a planet, 

subsequent observations show it expanding and fading until Hubble could no longer detect it. A team of researchers thinks it is actually a dust cloud left behind from a 

collision between two icy bodies. By now, the cloud is likely larger than Earth’s orbit around the Sun. 

Credit: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona) 

Learn more: https://hubblesite org/contents/news-releases/2020/news-2020-09 

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Tracing the Aftermath of a Cosmic Collision
 

Astronomers using Hubble thought they had captured an exoplanet, but subsequent results hint that it was actually a cloud of debris instead. The simulated image in 

the background of this video shows the star system without the central star’s light, making the surrounding features easier to see. The supposed planet was found 

orbiting near a large dust ring. The animated inset zooms in on the object and simulates how it expanded and faded, based on several years of Hubble observations. 

Researchers consider this evidence of the aftermath of a titanic collision between two icy bodies. 

Credit: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona) 

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Gathering Evidence of a Planet Flinging Comets Into a 

Young Star 

As Hubble’s images of the comet Shoemaker-Levy 9 impact on Jupiter “These star-grazing 

help illustrate, Jupiter sometimes serves as Earth’s protector by blocking or 

comets may make life deflecting objects that could collide with our planet. But the reverse can be 

true, too; when our solar system was younger, the giant planet also hurled possible, because they 

asteroids and comets in Earth’s direction, toward the Sun. Astronomers using 

carry water and other Hubble recently found clues that something similar is happening around the 

young star HD 172555––a Jupiter-sized planet seems to be flinging comets life-forming elements to 

toward its star. 

terrestrial planets.” 

Scientists didn’t see either the planet or comets directly, but pieced this Carol Grady, Eureka Scientific Inc. and NASA Goddard 

explanation together from various lines of evidence. First, a team of French Space Flight Center 

astronomers mined archival data gathered by the European Southern 

Observatory and found the chemical fingerprints of calcium imprinted in HD 

172555’s light––evidence of comet-like objects plunging into the star. Then another group of astronomers followed 

up by using Hubble to conduct a spectrographic analysis in ultraviolet light. Hubble detected fast-moving silicon and 

carbon gas in the starlight. The most likely explanation for the speedy gas is that material from the comets vaporized 

after streaking across the star’s disk. 

Astronomers consider this circumstantial evidence for gravitational stirring by an unseen Jupiter-size planet, where 

comets deflected by the massive object’s gravity are catapulted into the star. This is the same mechanism that may 

have transported water to Earth and the other inner planets of our solar system. HD 172555 is the third extrasolar 

system where astronomers have detected doomed, wayward comets, and all three systems are young. Studying them 

offers insight into what probably happened in the early days of our own solar system. 

This illustration shows an enormous disk of dusty material surrounding the young star HD 172555. Astronomers using Hubble found evidence that comets are falling in 

toward the star when they detected gas that is likely the vaporized remnants of the icy comet cores. The gas was moving at about 360,000 miles per hour across the 

face of the star. The gravitational influence of a suspected Jupiter-size planet in the foreground may have catapulted the comets into the star. 

Credit: NASA, ESA, and A. Feild and G. Bacon (STScI) 

Learn more: https://hubblesite.org/contents/news-releases/2017/news-2017-02.html 

45 
Puzzling Out the Atmosphere of a Mid-Size World
 

Kepler Space Telescope surveys suggest that the most common type of “We don’t have anything 

planet found in the Milky Way’s disk doesn’t resemble any of the worlds in 

like this in the solar our own solar system, but is instead something like an Earth-Neptune hybrid 

Hubble teamed up with the Spitzer Space Telescope to study the detailed system, and that’s what 

spectroscopic fngerprint of the atmosphere of one such world, dubbed GJ 

makes it striking ” 3470 b, for the frst time to learn more about the nature and origin of these 

prevalent planets Björn Benneke, University of Montreal 

GJ 3470 b weighs in at nearly 13 times Earth’s mass and orbits its host red dwarf star in just three days Astronomers 

enlisted the combined multi-wavelength capabilities of Hubble and Spitzer to determine the composition of the wild 

world’s atmosphere They discovered that the planet has clear skies with only thin hazes, which allowed them to probe 

deep into the atmosphere They expected to see an atmosphere enriched with plenty of heavier elements like oxygen 

and carbon, possibly incorporated in water vapor molecules and methane gas However, they found mainly hydrogen 

and helium in the atmosphere, similar to the Sun’s makeup 

Astronomers think star-hugging planets typically formed farther from their host star and then migrated inward over time 

However, in GJ 3470 b’s case, the planet may have formed in place as a large rocky core that then accumulated hydrogen 

from a primordial disk of gas around its star when the star was very young The disk may have dissipated before the planet 

could bulk up further The James Webb Space Telescope will be able to probe even deeper into GJ 3470 b’s atmosphere 

thanks to its unprecedented sensitivity to infrared light, possibly unveiling even more about this perplexing planet 

Hubble and Spitzer revealed tantalizing clues about the chemical nature of a mid-size planet, GJ 3740 b, which is between the masses of Earth and Neptune. The 

planet has a large rocky core buried under a crushing atmosphere of hydrogen and helium. Astronomers think it was able to accrete hydrogen from the disk that 

surrounded the young star, but the disk may have dissipated before the planet accumulated enough material to become a hot Jupiter. 

Credit: NASA, ESA, and L. Hustak (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2019/news-2019-38 html 

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Measuring a Giant Planet’s Growth 

Hubble has primarily found fully-formed planets, but a new study shows that “This is the youngest bona 

the observatory can also identify worlds that are still growing Researchers fde planet Hubble has homed in on a young system called PDS 70, located 370 light-years from 

Earth The central star is surrounded by a primordial disk of gas and dust that ever directly imaged ” 

provides fuel to feed the growth of orbiting planets The team directly imaged 

Yifan Zhou, University of Texas at Austin the giant world PDS 70b in ultraviolet light––something that had never been 

done before––and spotted radiation from extremely hot gas falling onto the 

planet The observation provided a way to estimate how quickly the planet is growing No other telescope is currently 

capable of making such high-sensitivity measurements in ultraviolet light 

PDS 70b has been amassing material for about fve million years and has already bulked up to fve times Jupiter’s mass 

However, it may be nearing the end of its formation process Researchers found that the planet is building up mass 

so slowly now that if the rate remains steady for another million years, its bulk will only increase by about 1/100th of 

Jupiter’s mass 

The study relied on a novel observing strategy and post-processing technique designed to overcome the glare from the 

host star, which is 3,000 times brighter than the planet in ultraviolet light The team’s results offer a new way to study 

how giant planets grow out of circumstellar disks around other stars Future observations could reveal how much of the 

gas and dust in such disks fall onto their planets, and whether the process occurs at a steady rate While ground-based 

telescopes and the James Webb Space Telescope will be able to help measure PDS 70b’s growth rate in visible and 

infrared light, Hubble’s unique ultraviolet observations remain critical for studying planet formation because the process 

is mostly visible in ultraviolet 

This Hubble image shows the giant world dubbed PDS 70b, marking the frst time an exoplanet was directly imaged in ultraviolet light. Astronomers used a 

coronagraph on Hubble’s camera to block out the glare from the planet’s host star. The observation revealed radiation from super-heated gas falling onto the world, 

offering a way to estimate how quickly the planet is growing. 

Credit: NASA, ESA, McDonald Observatory–University of Texas, Yifan Zhou (UT), Joseph DePasquale (STScI) 

Learn more: https://hubblesite org/contents/news-releases/2021/news-2021-021 

47 
This illustration of the exoplanet PDS 70b shows how the giant planet is growing. Material that forms the disk around the world’s host star is being siphoned by the 

planet, creating a smaller disk within the larger circumstellar disk. By employing Hubble’s ultraviolet light sensitivity, researchers took a unique look at radiation from 

extremely hot gas falling onto the planet, allowing them to directly measure the planet’s growth rate for the frst time. 

Illustration credit: NASA, ESA, STScI, Joseph Olmsted (STScI) 

48 
SUMMARY
 

The Hubble Space Telescope launched in 1990, two years before the frst exoplanets were announced Though the 

observatory was not designed with exoplanet science in mind, it has revealed exceedingly valuable information about 

hundreds of other worlds Thanks to its location in space, Hubble does not have to look through Earth’s turbulent 

atmosphere, which distorts images and largely blocks infrared and ultraviolet light And Hubble’s unique ultraviolet-light 

capabilities help astronomers study planetary atmospheres and environments in greater depth 

Using Hubble, astronomers probed an exoplanet’s atmosphere for the frst time more than 20 years ago Now, such 

Hubble observations have extended to Earth-size worlds and have even identifed atmospheres that contain sodium, 

oxygen, carbon, hydrogen, carbon dioxide, methane, and water vapor While most of the planets Hubble has studied to 

date are too hot to host life as we know it, the telescope’s observations demonstrate that the basic organic components 

for life can be detected and measured on planets orbiting other stars, setting the stage for more detailed studies with 

future observatories 

Over just the last several years, Hubble has confrmed that a planet orbits two suns, and made a detailed global map of 

another world showing the temperature at different layers in its atmosphere and the amount and distribution of its water 

vapor The observatory has revealed a cosmic case of mistaken identity and uncovered an immense cloud of hydrogen 

bleeding off a nearby world Perhaps most exciting of all, Hubble has identifed water vapor on planets that orbit in their 

star’s habitable zone Other current and future missions, including the James Webb Space Telescope, will follow up 

and build on some of Hubble’s most compelling fndings, offering complementary information and even more detailed 

views The mission’s ongoing observations will continue to enhance our understanding of the cosmos and reveal new 

planetary wonders, propelling us forward in our search for life on other planets 

A hot Jupiter is nearly aligned with its host star in this artist’s illustration. Such planets are ideal candidates for Hubble to study because astronomers can gather 

precise measurements of the chemical composition of planetary atmospheres as starlight flters through them. 

Credit: NASA, ESA, and G. Bacon (STScI) 

49 
MORE INFORMATION
 

For more information about the Hubble Space Telescope mission and its discoveries, visit NASA’s Hubble website at 

nasa gov/hubble For additional details and resources, visit HubbleSite org 

Follow Hubble’s exploration of exoplanets at the following social media sites 

Facebook 

https://www facebook com/NASAHubble 

Twitter 

https://twitter com/NASAHubble 

Instagram 

https://www instagram com/NASAHubble 

YouTube 

https://www youtube com/playlist?list=PL3E861DC9F9A8F2E9 

Flickr 

https://www fickr com/photos/nasahubble 

Pinterest 

https://www pinterest com/nasa/hubble-space-telescope/ 

Two planets are transiting, or passing in front of, their host star in this illustration. Hubble studies exoplanet atmospheres spectroscopically during transits, helping 

astronomers understand what the atmospheres are made of. This offers clues to the planets’ formation and evolution and hints at whether they are likely to be 

habitable. 

Credit: NASA, ESA, and G. Bacon (STScI) 

50 
CREDITS
 

The Hubble Space Telescope is a cooperative project between the National Aeronautics and Space Administration 

(NASA) and the European Space Agency (ESA). The Hubble Space Telescope Operations Project at the NASA Goddard 

Space Flight Center (GSFC) manages the mission. The Space Telescope Science Institute (STScI), operated by the 

Association of Universities for Research in Astronomy (AURA), conducts Hubble’s science operations and Lockheed 

Martin conducts Hubble’s mission operations, both under contracts with NASA. 

Hubble Focus: Strange New Worlds was produced by GSFC. It was published in June 2022. 

The production team for this book included Ashley Balzer (writer), Katrina Fajardo, Ed Henderson, and Mike Marosy 

(designers), Ken Carpenter and Jennifer Wiseman (science advisors), Vanessa Thomas, Kevin Hartnett, James Jeletic, 

and Andrea Gianopoulos (editors) at GSFC. 

This illustration gives an impression of how common planetary systems are. Astronomers have discovered that there are even more planets than stars in our Milky 

Way galaxy. The planets, their orbits, and their host stars are all vastly magnified to make them visible in this image. Studying these worlds using Hubble helps us 

understand more about the universe and our place within it. 

Credit: NASA, ESA, and M. Kornmesser (ESO) 

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