remiconnesson/oceanservice-noaa-facts huggingface dataset:
# Are there oceans on other planets?

![Europa](/facts/et-oceans.jpg "One of Jupiter's fifty known moons, Europa has an icy surface and is thought to have subsurface liquid water. ")

_Europa may have subsurface liquid water. Scientists hypothesize that Europa's hidden ocean is salty, tidal, and causes its ice surface to move, resulting in large fractures that are clearly visible. Although Europa lies outside of our solar system's habitable zone, it may have the [ingredients needed to support life](https://europa.nasa.gov/why-europa/ingredients-for-life/) — water, energy, and organic compounds. (Image Credit: NASA/JPL/Ted Stryk)._

Evidence points to oceans on other planets and moons, even within our own solar system. But Earth is the only known planet (or moon) to have consistent, stable bodies of liquid water on its _surface._ In our solar system, Earth orbits around the sun in an area called the [habitable zone](https://exoplanets.nasa.gov/search-for-life/habitable-zone/). The temperature within this zone, along with an ample amount of atmospheric pressure, allow water to be liquid for long periods of time.

Scientists believe several moons within our solar system have significant [subsurface liquid water deposits](https://www.nasa.gov/specials/ocean-worlds/). Saturn’s moon Enceladus and Jupiter’s moon Europa are two examples. Both appear to have salty, liquid oceans covered with thick layers of ice at the surface. Scientists have observed water plumes erupting from Enceladus, and believe similar plumes can be found on Europa. The existence of these geysers also tells scientists that these moons have a source of energy, perhaps from gravitational forces or radiation — energy that keeps the oceans liquid under the ice and could even support life.

Beyond our solar system, scientists have found thousands of [exoplanets](https://exoplanets.nasa.gov/) — planets that orbit other stars — including some in the habitable zone. Using mathematical models, researchers estimate that more than [a quarter of known exoplanets](https://www.nasa.gov/feature/goddard/2020/are-planets-with-oceans-common-in-the-galaxy-it-s-likely-nasa-scientists-find) may have liquid water, though the majority would have subsurface oceans like those on Europa and Enceladus.

The search for liquid water is critical to the [search for life beyond Earth](https://exoplanets.nasa.gov/search-for-life/can-we-find-life/). While scientists originally focused the search on finding planets with liquid water on their surface, that thinking is changing. Here on Earth, we have examples of life flourishing in some of the most extreme conditions, such as the complex ecosystems around [hydrothermal vents](https://oceanservice.noaa.gov/facts/vents.html) on the seafloor. Scientists are reconsidering whether life could exist below an icy surface, even within our solar system on moons like Europa and Enceladus.
# Was Moby Dick a real whale?

![Illustrations from Moby-Dick, published in 1851 and authored by Herman Melville.](/facts/mobydick.jpg "Illustrations from Moby-Dick, published in 1851 and authored by Herman Melville.")

_Illustrations from "Moby-Dick", published in 1851 and authored by Herman Melville._

##### Did you know?

_In 2011, maritime heritage archaeologists working with NOAA’s Office of National Marine Sanctuaries found the wreckage of _Two Brothers_ located nearly six hundred miles northwest of Honolulu._

"Moby-Dick; or, The Whale", the allegorical novel about Captain Ahab’s search to kill a great white whale, was based on real-life events. Born in 1819, author Herman Melville grew up during the peak of American dominance of the whaling industry, roughly the period between 1820 and the start of the Civil War. Weaving contemporary accounts and his own experiences as a whaler, Melville created his American masterpiece.

The young Melville was famously inspired by the story of George Pollard, the former captain of the whaler _Essex_. While on a two-year whaling expedition crisscrossing the Pacific, the _Essex_ was rammed by a sperm whale. Quickly abandoning ship and thousands of miles from land, Pollard and his crew escaped in leaky lifeboats to begin a horrific ordeal resulting in sickness, starvation, and cannibalism. One of the few to survive, Pollard was given a second chance at captaining another whaler, the [_Two Brothers._](http://www.papahanaumokuakea.gov/maritime/twobrothers.html) But after 18 months in the Pacific, Pollard ran the _Two Brothers_ aground, sinking the ship in what is now the [Papahānaumokuākea Marine National Monument.](http://www.papahanaumokuakea.gov/about/)

The name of the whale was also inspired by real-life events. In 1839, Melville read a story in a magazine about an albino sperm whale famed for its deadly attacks on whaling ships trying to hunt it down. This whale, killed off the coast of Chile near Mocha Island, was called Mocha Dick.

Did you know? - *In 2011, maritime heritage archaeologists working with NOAA’s Office of National Marine Sanctuaries found the wreckage of *Two Brothers* located nearly six hundred miles northwest of Honolulu.*
# What is a bivalve mollusk?

## Bivalve mollusks (e.g., clams, oysters, mussels, scallops) have an external covering that is a **two-part hinged shell** that contains a soft-bodied invertebrate.

![Bivalve mollusks (e.g., clams, oysters, mussels, scallops) ](bivalvemollusk.jpg "What is a bivalve mollusk?")

A roughfile clam from the Flower Garden Bank National Marine Sanctuary—just one of many different bivalve mollusk species.

Like fish, bivalve mollusks breathe through their gills. As filter feeders, bivalves gather food through their gills. Some bivalves have a pointed, retractable "foot" that protrudes from the shell and digs into the surrounding sediment, effectively enabling the creature to move or burrow.

Bivalves even make their own shells. An internal organ called the mantle secretes calcium carbonate so that as the inner invertebrate grows, the outer shell provides a roomier home.

Many bivalve species play important roles in aquatic and marine ecosystems by filtering the water and serving as habitat and prey for a variety of sea life. This diverse group of species, estimated at about 9,200, inhabits virtually the entire world ocean, from the balmy tropics to the sub-zero Arctic, and from the deep ocean to sandy and rocky shorelines. A few have even taken up residence around hydrothermal vents found deep in the Pacific Ocean, below 13,000 feet.

If the bivalve's biological brilliance alone fails to impress, then consider that NOAA estimated the 2011 economic value of commercial bivalve mollusk harvesting at about $1 billion annually in the U.S., and the weight of the harvest was estimated at 153.6 million pounds.
# Is the Earth round?

![Earth from space](/facts/earth-round.jpg "A view of the Earth from space.")

_This [NASA image](http://earthobservatory.nasa.gov/IOTD/view.php?id=885) shows Earth from space. The image is a combination of data from two satellites. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard NASA’s [Terra](http://terra.nasa.gov/) satellite collected the land surface data over 16 days, while NOAA’s [Geostationary Operational Environmental Satellite](http://www.goes.noaa.gov/) (GOES) produced a snapshot of the Earth’s clouds._

While the Earth appears to be round when viewed from the vantage point of space, it is actually closer to an ellipsoid. However, even an ellipsoid does not adequately describe the Earth’s unique and ever-changing shape.

Our planet's diameter bulges at the equator due to the centrifugal force created by the earth’s constant rotation. Mountains rising almost [30,000 feet](#) and ocean trenches diving over [36,000 feet](#)(compared to [sea level](https://tidesandcurrents.noaa.gov/sltrends/faq.shtml)) further distort the shape of the Earth. _Sea level_ itself is even irregularly shaped. Slight variations in Earth’s gravity field cause permanent hills and valleys in the ocean’s surface of over [300 feet](#).

Additionally, the shape of the Earth is always changing. Sometimes this change is periodic, as is the case with daily tides that affect both the ocean and the crust; sometimes the change is slow and steady, as with the drift of tectonic plates or the [rebound of the crust after a heavy sheet of ice has melted](/facts/glacial-adjustment.html); and sometimes the shape of the planet changes in violent, episodic ways during events such as earthquakes, volcanic eruptions, or meteor strikes.

The [National Geodetic Survey](http://geodesy.noaa.gov/) measures and monitors our ever-changing planet. [Geodesy](geodesy.html) is the science of measuring and monitoring the size and shape of the Earth, including its gravity field, and determining the location of points on the Earth’s surface.
# What is Ocean Acidification?

## Ocean acidification refers to a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere.

 [](/facts/ocean-acidification.mp4) 

What is ocean acidification? Watch our video for a quick overview.

For more than 200 years, or since the industrial revolution, the concentration of carbon dioxide (CO2) in the atmosphere has increased due to the burning of fossil fuels and land use change. The ocean absorbs about 30 percent of the CO2 that is released in the atmosphere, and as levels of atmospheric CO2 increase, so do the levels in the ocean.

When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant.

Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.

These changes in ocean chemistry can affect the behavior of non-calcifying organisms as well. Certain fish's ability to detect predators is decreased in more acidic waters. When these organisms are at risk, the entire food web may also be at risk.

Ocean acidification is affecting the entire world’s oceans, including coastal estuaries and waterways. Many economies are dependent on fish and shellfish and people worldwide rely on food from the ocean as their primary source of protein.
# What is the most venomous marine animal?

## The **Australian box jellyfish** is considered the most venomous marine animal.

![photo of box jellyfish](box-jellyfish.jpg "photo of box jellyfish")

Carybdea branchi, pictured here, is a relative of the Australian box jellyfish (_Chironex fleckeri_), which is considered the most venomous marine animal. (Image courtesy of Brent Viljoen)

They may not look dangerous, but the sting from a box jellyfish could be enough to send you to Davy Jones's locker-a watery grave, that is.

Box jellyfish, named for their body shape, have tentacles covered in biological booby traps known as nematocysts - tiny darts loaded with poison. People and animals unfortunate enough to be injected with this poison may experience paralysis, cardiac arrest, and even death, all within a few minutes of being stung. But don’t choose the mountains over the ocean just yet. Of the 50 or so species of box jellyfish, also called sea wasps, only a few have venom that can be lethal to humans.

While box jellyfish are found in warm coastal waters around the world, the lethal varieties are found primarily in the Indo-Pacific region and northern Australia. This includes the Australian box jellyfish (_Chironex fleckeri_), considered the most venomous marine animal. _Chironex fleckeri_ is the largest of the box jellyfish, with body sizes reaching up to one foot in diameter and thick, bootlace-like tentacles up to 10 feet long.

Box jellyfish have traits that set them apart from other jellyfish. Most notably, box jellyfish can swim—at maximum speeds approaching four knots—whereas most species of jellyfish float wherever the current takes them, with little control over their direction. Box jellyfish can also see. They have clusters of eyes on each side of the box. Some of these eyes are surprisingly sophisticated, with a lens and cornea, an iris that can contract in bright light, and a retina.

Their speed and vision leads some researchers to believe that box jellyfish actively hunt their prey, mainly shrimp and small fish.
# What are spring and neap tides?

![graphic showing orbit of moon around Earth, illustrating spring and neap tides](/facts/springtide.gif)

_A spring tide is a common historical term that has nothing to do with the season of spring. Rather, the term is derived from the concept of the tide "springing forth." Spring tides occur twice each lunar month all year long without regard to the season. Neap tides, which also occur twice a month, happen when the sun and moon are at right angles to each other._

Tides are long-period waves that roll around the planet as the ocean is "pulled" back and forth by the gravitational pull of the moon and the sun as these bodies interact with the Earth in their monthly and yearly orbits.

During full or new moons—which occur when the Earth, sun, and moon are nearly in alignment—average tidal ranges are slightly larger. This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is "added" to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are a little higher and low tides are a little lower than average.

These are called **spring tides**, a common historical term that has nothing to do with the season of spring. Rather, the term is derived from the concept of the tide "springing forth." Spring tides occur twice each lunar month all year long, without regard to the season.

Seven days after a spring tide, the sun and moon are at right angles to each other. When this happens, the bulge of the ocean caused by the sun partially cancels out the bulge of the ocean caused by the moon. This produces moderate tides known as **neap tides**, meaning that high tides are a little lower and low tides are a little higher than average. Neap tides occur during the first and third quarter moon, when the moon appears "half full."

NOAA’s [tide and tidal current predictions](https://tidesandcurrents.noaa.gov/tide_predictions.shtml) take into account astronomical considerations due to the position of the moon and the sun.
# Why do ships use 'port' and 'starboard' instead of 'left' and 'right?'

![image of port side of NOAA Ship Fairweather](/facts/port-starboard.jpg " 'port' and 'starboard' refer to fixed locations on a vessel.")

_Port side of NOAA Ship Fairweather._

Since port and starboard never change, they are unambiguous references that are independent of a mariner’s orientation, and, thus, mariners use these nautical terms instead of left and right to avoid confusion. When looking forward, toward the bow of a ship, port and starboard refer to the left and right sides, respectively.

In the early days of boating, before ships had rudders on their centerlines, boats were controlled using a steering oar. Most sailors were right handed, so the steering oar was placed over or through the right side of the stern. Sailors began calling the right side the steering side, which soon became "starboard" by combining two Old English words: _stéor_ (meaning "steer") and _bord_ (meaning "the side of a boat").

As the size of boats grew, so did the steering oar, making it much easier to tie a boat up to a dock on the side opposite the oar. This side became known as larboard, or "the loading side." Over time, larboard—too easily confused with starboard—was replaced with port. After all, this was the side that faced the port, allowing supplies to be ported aboard by porters.
# Are mermaids real?

## No evidence of aquatic humanoids has ever been found.

![description of image](mermaid.jpg "short caption")

Statue of a sailor mermaid from Portsmouth, Virginia.

Mermaids — those half-human, half-fish sirens of the sea — are legendary sea creatures chronicled in maritime cultures since time immemorial. The ancient Greek epic poet Homer wrote of them in _The Odyssey_. In the ancient Far East, mermaids were the wives of powerful sea-dragons, and served as trusted messengers between their spouses and the emperors on land. The aboriginal people of Australia call mermaids _yawkyawks_ – a name that may refer to their mesmerizing songs.

The belief in mermaids may have arisen at the very dawn of our species. Magical female figures first appear in cave paintings in the late Paleolithic (Stone Age) period some 30,000 years ago, when modern humans  gained dominion over the land and, presumably, began to sail the seas. Half-human creatures, called chimeras, also abound in mythology — in addition to mermaids, there were wise centaurs, wild satyrs, and frightful minotaurs, to name but a few.

But are mermaids real? No evidence of aquatic humanoids has ever been found. Why, then, do they occupy the collective unconscious of nearly all seafaring peoples? That’s a question best left to historians, philosophers, and anthropologists.
# What is the difference between a threatened and endangered species?

##### **Did you know?**

_The ESA provides for the conservation of species that are endangered or threatened. There are approximately 2,150 total species listed under the ESA. NOAA's National Marine Fisheries Service and the U.S. Fish and Wildlife Service share responsibility for implementing the ESA._

The [Endangered Species Act](https://www.fisheries.noaa.gov/national/endangered-species-conservation/endangered-species-act) (ESA) defines an endangered species as "any species which is in danger of extinction throughout all or a significant portion of its range." Endangered species are automatically protected by prohibitions of several types of "take," including harming, harassing, collecting, or killing, under Section 9 of the ESA. There are some limited exceptions to these rules listed in Section 10 of the ESA. The Kemp's ridley turtle, considered the smallest marine turtle in the world, is listed as an endangered species throughout its range of the Gulf of America and entire U.S. Atlantic seaboard.

The ESA defines a threatened species as "any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." Threatened species receive protections through separate regulations issued under Section 4(d) of the ESA. These regulations occur separately from the listing and detail what take prohibitions are in effect. Also called 4(d) rules, they can include the same prohibitions under Section 9. Elkhorn coral – a large, branching coral with thick and sturdy antler-like branches – is listed as a threatened species throughout its range.

NOAA scientists use the best scientific and commercial information available as the basis for their listing decisions. Scientists may not consider the economic impact of listing a particular species. A species must be listed if it is threatened or endangered due to any of the following five factors:

Did you know? - *The ESA provides for the conservation of species that are endangered or threatened. There are approximately 2,150 total species listed under the ESA. NOAA's National Marine Fisheries Service and the U.S. Fish and Wildlife Service share responsibility for implementing the ESA.*
# What is the difference between a hurricane watch and a warning?

![A close-up satellite image of Hurricane Isabel taken on Sept. 15, 2003. ](/facts/cyclone1.jpg "A close-up satellite image of Hurricane Isabel taken on Sept. 15, 2003. ")

_A close-up satellite image of Hurricane Isabel taken on Sept. 15, 2003. The National Ocean Service helps coastal communities prepare for and recover from major coastal storms such as hurricanes._

Hurricane warnings indicate that hurricane conditions (sustained winds of 74 mph or higher) are _**expected**_ somewhere within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force (sustained winds of 39 to 73 mph), the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds to allow for important preparation.

**During a hurricane warning, complete storm preparations and immediately leave the threatened area if directed by local officials**.

A hurricane watch means that hurricane conditions (sustained winds of 74 mph or higher) are _**possible**_ within the specified area. A hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds in an area.

**During a hurricane watch, prepare your home and review your plan for evacuation in case a hurricane or tropical storm warning is issued. Listen closely to instructions from local officials**.
# What is sea foam?

![Sea Foam at Ocean Beach in San Francisco. Image credit: Brocken Inaglory, Wikipedia](/facts/seafoam.jpg "Sea foam forms when dissolved organic matter in the ocean is churned up")

_Sea Foam at Ocean Beach in San Francisco._

If you scoop up some water from the ocean in a clear glass and look at it closely, you'll see that it's chock full of tiny particles. Seawater contains dissolved salts, proteins, fats, dead algae, detergents and other pollutants, and a bunch of other bits and pieces of organic and artificial matter. If you shake this glass of ocean water vigorously, small bubbles will form on the surface of the liquid.

Sea foam forms in this way - but on a much grander scale - when the ocean is agitated by wind and waves. Each coastal region has differing conditions governing the formation of sea foams.

Algal blooms are one common source of thick sea foams. When large blooms of algae decay offshore, great amounts of decaying algal matter often wash ashore. Foam forms as this organic matter is churned up by the surf.

Most sea foam is not harmful to humans and is often an indication of a productive ocean ecosystem. But when large harmful algal blooms decay near shore, there are potential for impacts to human health and the environment. Along Gulf coast beaches during blooms of Karenia brevis, for example, popping sea foam bubbles are one way that algal toxins become airborne. The resulting aerosol can irritate the eyes of beach goers and poses a health risk for those with asthma or other respiratory conditions. Scientists studying the cause of a seabird die-offs off California in 2007 and in the Pacific Northwest in 2009 also found a soap-like foam from a decaying _Akashiwo sanguinea_ algae bloom had removed the waterproofing on feathers, making it harder for birds to fly. This led to the onset of fatal hypothermia in many birds.