{"id":143333,"date":"2018-11-20T15:00:00","date_gmt":"2018-11-20T19:00:00","guid":{"rendered":"https:\/\/www.nasa.gov\/?migration=converted-node-436023"},"modified":"2023-07-26T15:13:47","modified_gmt":"2023-07-26T19:13:47","slug":"nasa-retires-prolific-solar-observatory-after-16-years","status":"publish","type":"post","link":"https:\/\/www.nasa.gov\/missions\/rhessi\/nasa-retires-prolific-solar-observatory-after-16-years\/","title":{"rendered":"NASA Retires Prolific Solar Observatory After 16 Years"},"content":{"rendered":"\n<p>Every morning for the past 16 years, solar physicist S\u00e4m Krucker sat down at his desk to check the latest data from NASA\u2019s RHESSI. Had the solar observatory seen a flare overnight? If there was a new flare, Krucker, RHESSI principal investigator at University of California, Berkeley, since 2013, would pore over the data, each recorded X-ray telling him something about the giant explosion on the Sun.<\/p>\n\n\n\n<p>Now, many years after launching on Feb. 5, 2002, the RHESSI \u2014 short for Reuven Ramaty High Energy Solar Spectroscopic Imager \u2014 mission has ended; Krucker, and many other scientists, will no longer check the spacecraft\u2019s data returns each day. In anticipation of losing touch with the spacecraft\u2019s aging receiver, mission operators sent the spacecraft commands to decommission on Aug. 16, 2018.<\/p>\n\n\n\n<p>\u201cIt does impact everyday life that way,\u201d Krucker said. Though it\u2019s appropriate timing for RHESSI to stop operations now, he said, while the Sun nears solar minimum, the lull in its activity over an approximately 11-year cycle. \u201cThe next two to three years would have been quite boring.\u201d<\/p>\n\n\n<div id=\"\" class=\"hds-media hds-module wp-block-image\"><div class=\"margin-left-auto margin-right-auto nasa-block-align-wide\"><div class=\"hds-media-wrapper margin-left-auto margin-right-auto\"><figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-none \"><a href=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1041\" height=\"585\" src=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif?w=1041\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"animation of RHESSI satellite\" style=\"transform: scale(1); transform-origin: 50% 50%; object-position: 50% 50%; object-fit: cover;\" block_context=\"nasa-block\" loading=\"eager\" \/><\/a><\/figure><figcaption class=\"hds-caption padding-y-2\"><div class=\"hds-caption-text p-sm margin-0\">An artist\u2019s representation of RHESSI. Flying up above Earth\u2019s radiation-blocking atmosphere, RHESSI could observe X-rays and gamma rays from solar flares.<\/div><div class=\"hds-credits\"><strong><em>Credits: NASA<\/em><\/strong><\/div><\/figcaption><\/div><\/div><\/div>\n\n\n<p>RHESSI\u2019s job was to watch the Sun for solar flares, some of the most dramatic events on the Sun that can sometimes fling solar energy toward Earth.<\/p>\n\n\n\n<p>During a flare, gas in the Sun\u2019s atmosphere rapidly soars over 20 million degrees Fahrenheit, sending particles flying at near-light speeds. In turn, the particles emit high-energy emissions like X-rays and even higher gamma rays, which we can detect from far away. These rays can\u2019t, however, penetrate Earth\u2019s atmosphere and be measured from the ground, so RHESSI observed them from space. In doing so, RHESSI aimed to understand how flares work, the physics underlying how the Sun generates such powerful bursts of energy.<\/p>\n\n\n\n<p>Ask any scientist who worked on RHESSI what their favorite flare is, and they\u2019ll easily rattle off a date, as if it\u2019s a birthday or holiday they\u2019ll always remember. Krucker said his favorite is either Jan. 20, 2005, or July 19, 2012. Mission scientist Brian Dennis at NASA\u2019s Goddard Space Flight Center in Greenbelt, Maryland, said April 21, 2002, RHESSI\u2019s very first X-class flare \u2014 the strongest type. For them, these are special dates because RHESSI taught them something new that day.<\/p>\n\n\n\n<p>\u201cWhen I first looked at the Jan. 20 flare and saw where the high energy was coming from, that brought my understanding to the next level,\u201d Krucker said. \u201cOne guy even has a most-hated flare. He had many arguments with colleagues over it, trying to explain it, which was not always pleasurable.\u201d<\/p>\n\n\n\n<p>Throughout the course of its mission, RHESSI saw more than 75,000 solar flares. These observations have helped scientists craft and refine a model of how solar eruptions form. Launching in early 2002, just after the Sun reached solar maximum in 2001, the spacecraft was poised to see many flares.<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"RHESSI Observes Solar Flare Over AR9906\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/Li8Pqlb4U3Y?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><figcaption class=\"wp-element-caption\">Observations from RHESSI and another NASA mission TRACE are combined in these images of a powerful flare on April 21, 2002.<br><strong><em>Credits: NASA Goddard\/RHESSI\/TRACE<br><\/em><\/strong><a href=\"https:\/\/svs.gsfc.nasa.gov\/2462\" rel=\"noopener\">Download this video from NASA Goddard’s Scientific Visualization Studio<\/a><\/figcaption><\/figure>\n\n\n\n<p>\u201cHigh energies are always interesting in astronomy,\u201d University of Minnesota solar scientist Lindsay Glesener said. \u201cThey\u2019re the biggest explosions, the hottest plasma. But flares are going on at our Sun, which is right next to us and affects us in lots of ways. When I was a grad student, it took just one conversation with Robert Lin, the principal investigator from 2002 to 2012, to convince me flares are the most fascinating thing in the universe.\u201d<\/p>\n\n\n\n<p>To understand how solar flares erupt from the Sun, you have to know where their energy comes from. For this, RHESSI carried just one instrument, called an imaging spectrometer, capable of recording both X-rays and gamma rays. For scientists, these high-energy emissions are like fingerprints, showing them how each eruption unfolds: X-rays are associated with electron activity, while gamma rays come from protons and ions.<\/p>\n\n\n\n<p>The instrument combined images of the Sun with its spectroscopy to show all the different energy levels in the flare. This allows scientists to map out where energy comes from during an explosion, and what\u2019s producing that energy.<\/p>\n\n\n\n<p>\u201cPrevious mission designs had two different instruments, but RHESSI was able to study this large energy range in X-rays and gamma rays, all with the same instrument,\u201d said Albert Shih, RHESSI deputy mission scientist at Goddard. \u201cIt was an innovative design, and a lot of good science came of it.\u201d<\/p>\n\n\n\n<p>RHESSI\u2019s observation of so many flares over the years, from one solar cycle to the next, broke new ground in solar physics and enabled a much deeper understanding of flares \u2014 where they accelerate particles, and just how much they can vary in scale, from tiny nanoflares to massive superflares, tens of thousands of times bigger and more explosive. <\/p>\n\n\n\n<p>\u201cRHESSI had several firsts,\u201d Dennis said. \u201cNo one had ever imaged X-rays at this high an energy level before, or imaged gamma rays at all. RHESSI made great strides by making energy measurements with higher resolution than had previously been possible.\u201d<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Solar Flares Aren\u2019t Simple <\/strong><\/h3>\n\n\n\n<p>With these unprecedented capabilities, RHESSI gave scientists entirely novel information, revealing just how complex flares can be.<\/p>\n\n\n\n<p>Early RHESSI observations of a strong flare on April 15, 2002, showed X-rays coming from two different places at once: one high in the Sun\u2019s atmosphere and another lower down. Researchers interpreted this to mean a huge punch of energy occurred between the two spots.<\/p>\n\n\n\n<p>After tracking the energy in the two-sided explosion, they realized part of the explosion\u2019s energy shot high into the Sun\u2019s atmosphere and burst into a cloud of hot plasma to become a coronal mass ejection, while the other part bore down towards the surface, exploding into a flare. These explosions \u2014 the most powerful in the solar system \u2014 came to be known as solar eruptive events, in which the Sun\u2019s strongest flares and coronal mass ejections are linked, occurring at the same time.<\/p>\n\n\n\n<p>RHESSI introduced solar researchers to entirely new questions on the nature of flares. During an intense October 2003 flare, scientists noticed X-rays and gamma rays coming from two different places. Although electrons and ions have different masses, scientists expected them to originate from the same spot in the flare. Since each kind of emission reflects the presence of different kinds of particles, the unexpected disparity hinted at different mechanisms guiding the movements of each type of particle. Scientists still don\u2019t fully understand this process.<\/p>\n\n\n\n<p>\u201cThanks to RHESSI, we know much more about where particles are accelerated in flares,\u201d Glesener said. \u201cBut how they get accelerated remains a big mystery. RHESSI told us where we need to look in order to finish answering these questions.\u201d<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>The Shape of Our Star <\/strong><\/h3>\n\n\n\n<p>RHESSI\u2019s long-term data sets also led to findings that have nothing to do with flares at all. One major result concerned the shape of the Sun itself. Since it constantly spins, scientists expect the Sun, like Earth, to be a slightly flattened sphere with a bulging waistline. But pre-RHESSI measurements of the Sun determined it to be much flatter than theory dictated, raising questions of whether scientists had overlooked some crucial piece of information in their calculations.<\/p>\n\n\n\n<p>RHESSI put their confusion to rest through the routine information it gathered to assess where its instrument was pointing. To keep perfectly oriented, the spacecraft precisely recorded the position of the Sun\u2019s horizon 16 times per second. With such an extensive collection of data, scientists were able to determine the best ever <a href=\"https:\/\/science.nasa.gov\/science-news\/science-at-nasa\/2008\/02oct_oblatesun\" rel=\"noopener\">measurement of the Sun\u2019s shape<\/a> \u2014 and a close match to theoretical predictions.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Understanding Earth\u2019s Lightning Storms <\/strong><\/h3>\n\n\n\n<p>RHESSI\u2019s watch of gamma rays throughout the sky made it a prime tool to measure what are called terrestrial gamma-ray flashes, bursts of gamma rays emitted from high in Earth\u2019s atmosphere over lightning storms. The first of these had been spotted before, but RHESSI invigorated an entire field of study when it showed they are more common and luminous than previously thought. Current numbers suggest there may be as many as 400 bursts daily from thunderstorms at different locations around the world. The finding spurred new research, CubeSat observations and computer modeling.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>More Science to Come <\/strong><\/h3>\n\n\n<div id=\"\" class=\"hds-media hds-module wp-block-image\"><div class=\"margin-left-auto margin-right-auto nasa-block-align-inline\"><div class=\"hds-media-wrapper margin-left-auto margin-right-auto\"><figure class=\"hds-media-inner hds-cover-wrapper hds-media-ratio-none \"><a href=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/tgf_rhessi.gif\"><img loading=\"lazy\" decoding=\"async\" width=\"640\" height=\"480\" src=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/tgf_rhessi.gif?w=640\" class=\"attachment-2048x2048 size-2048x2048\" alt=\"RHESSI data on terrestrial gamma-ray sources\" style=\"transform: scale(1); transform-origin: 50% 50%; object-position: 50% 50%; object-fit: cover;\" block_context=\"nasa-block\" \/><\/a><\/figure><figcaption class=\"hds-caption padding-y-2\"><div class=\"hds-caption-text p-sm margin-0\">RHESSI not only viewed the Sun; it could detect gamma rays from sources on Earth as well. Each flash represents a terrestrial gamma-ray flash RHESSI observed over a several months.<\/div><div class=\"hds-credits\"><strong><em>Credits: NASA Goddard\/Tom Bridgman<\/em><\/strong><\/div><\/figcaption><\/div><\/div><\/div>\n\n\n<p>Throughout RHESSI\u2019s lifetime, scientists made the most of the mission by integrating its observations with those from other missions such as NASA\u2019s <a href=\"http:\/\/nasa.gov\/sdo\" rel=\"noopener\">Solar Dynamics Observatory<\/a> and <a href=\"http:\/\/nasa.gov\/stereo\" rel=\"noopener\">STEREO<\/a>, short for the Solar and Terrestrial Relations Observatory. Different instruments focus on different aspects of the Sun, or different levels of energy. By combining various vantage points across NASA\u2019s fleet of heliophysics spacecraft, researchers could piece together a holistic picture of the Sun\u2019s complex behavior. Scientists expect RHESSI will continue to shed light on flares for years to come, as they continue to parse its trove of data.<\/p>\n\n\n\n<p>With RHESSI no longer in operation, solar researchers do not currently have a way to monitor high-energy flare emissions. But new missions under development carry the torch of RHESSI\u2019s legacy.<\/p>\n\n\n\n<p>\u201cRHESSI established many young scientists, generating an entire class of high-energy solar physicists,\u201d Krucker said. \u201cIf you look at who\u2019s leading the next generation of X-ray telescopes now, they come from RHESSI science.\u201d<\/p>\n\n\n\n<p>Glesener and Shih both began their doctoral studies in solar physics with RHESSI data. Now, each is deeply involved with developing and testing advanced high-energy solar instruments for new missions \u2014 including the <a href=\"https:\/\/www.nasa.gov\/feature\/goddard\/2018\/nasa-funded-rocket-to-view-sun-with-x-ray-vision\" rel=\"noopener\">FOXSI sounding rocket<\/a> and <a href=\"https:\/\/www.nasa.gov\/feature\/goddard\/2016\/nasa-funded-balloon-launches-to-study-sun\" rel=\"noopener\">GRIPS high-altitude balloon<\/a>.<\/p>\n\n\n\n<p>\u201cThroughout its 16 years, it was RHESSI answering questions, but asking new ones along the way, that has motivated future missions,\u201d said Shih, who is also the GRIPS project scientist. \u201cRHESSI set the groundwork and framed our expectations for missions that will look at the Sun in even more detail as we investigate entirely new mysteries.\u201d <\/p>\n\n\n\n<p>RHESSI first launched as HESSI in February 2002, but was renamed just months after launch, in April that year, in memory of Reuven Ramaty, a deceased NASA scientist who had long championed the mission. The nominal two-year mission was first extended in 2004 for two years, and then extended several times more until its end.<\/p>\n\n\n\n<p>Currently, RHESSI is in a stable low-Earth orbit. But since it has no propulsion, atmospheric drag will continue to tug at its orbit until the satellite reenters Earth\u2019s atmosphere, which is expected to occur as early as 2022. NASA will monitor the satellite\u2019s deorbiting and reentry.<\/p>\n\n\n\n<p>RHESSI belongs to a class of NASA spacecraft called Small Explorers, missions that cost under $120 million with highly focused research goals. Goddard manages the Explorers Program for NASA\u2019s Heliophysics Division within the Science Mission Directorate at NASA Headquarters in Washington. The Explorers Program Office at Goddard provides management and technical oversight for RHESSI. RHESSI is a collaboration between Goddard, UC Berkeley, the Paul Scherrer Institute in Switzerland and General Dynamics in Arizona.<\/p>\n\n\n\n<h4 class=\"wp-block-heading\"><strong>Related: <\/strong><\/h4>\n\n\n\n<ul>\n<li><a href=\"https:\/\/hesperia.gsfc.nasa.gov\/rhessi3\/index.html\" rel=\"noopener\">NASA\u2019s RHESSI website<\/a><\/li>\n<\/ul>\n\n\n\n<p><strong><em>By <a href=\"mailto:lina.tran@nasa.gov?subject=RE%20RHESSI%20Decom\">Lina Tran<\/a><br><a href=\"http:\/\/nasa.gov\/goddard\" rel=\"noopener\">NASA\u2019s Goddard Space Flight Center<\/a>, Greenbelt, Md.<\/em><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Every morning for the past 16 years, solar physicist S\u00e4m Krucker sat down at his desk to check the latest data from NASA\u2019s RHESSI. Had the solar observatory seen a flare overnight? If there was a new flare, Krucker, RHESSI principal investigator at University of California, Berkeley, since 2013, would pore over the data, each [...]<\/p>\n","protected":false},"author":68,"featured_media":152570,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"nasa_hds_core_meta_l10n":"en-US","nasa_hds_core_meta_article_editor":"","nasa_hds_core_meta_article_contacts":[],"nasa_hds_core_meta_article_topic":"","nasa_hds_core_meta_linked_locations":[],"nasa_hds_core_meta_article_related_articles":[],"hds_migrate_meta_pr_release_id":"","hds_migrate_meta_pr_release_type":"","nasa_hds_core_meta_location_x":"","nasa_hds_core_meta_location_y":"","nasa_hds_core_meta_gallery_images":[],"footnotes":""},"categories":[2857,2837,3329,2772,2878,10795,9480,11310],"news-tags":[],"internal-terms":[3913,4025,10596],"coauthors":[],"parsely":{"version":"1.1.0","meta":{"@context":"https:\/\/schema.org","@type":"NewsArticle","headline":"NASA Retires Prolific Solar Observatory After 16 Years","url":"https:\/\/www.nasa.gov\/missions\/rhessi\/nasa-retires-prolific-solar-observatory-after-16-years\/","mainEntityOfPage":{"@type":"WebPage","@id":"https:\/\/www.nasa.gov\/missions\/rhessi\/nasa-retires-prolific-solar-observatory-after-16-years\/"},"thumbnailUrl":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif?w=150&h=150&crop=1","image":{"@type":"ImageObject","url":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif"},"articleSection":"NASA Centers & Facilities","author":[{"@type":"Person","name":"Abbey Interrante"}],"creator":["Abbey Interrante"],"publisher":{"@type":"Organization","name":"NASA","logo":"https:\/\/www.nasa.gov\/wp-content\/themes\/nasa\/assets\/images\/nasa-logo.svg"},"keywords":["The Solar System","The Sun","Goddard Space Flight Center","Heliophysics","Heliophysics Division","RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager)","Science Mission Directorate","Solar Flares","Space Weather"],"dateCreated":"2018-11-20T19:00:00Z","datePublished":"2018-11-20T19:00:00Z","dateModified":"2023-07-26T19:13:47Z"},"rendered":"<meta name=\"parsely-title\" content=\"NASA Retires Prolific Solar Observatory After 16 Years\" \/>\n<meta name=\"parsely-link\" content=\"https:\/\/www.nasa.gov\/missions\/rhessi\/nasa-retires-prolific-solar-observatory-after-16-years\/\" \/>\n<meta name=\"parsely-type\" content=\"post\" \/>\n<meta name=\"parsely-image-url\" content=\"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif?w=150&h=150&crop=1\" \/>\n<meta name=\"parsely-pub-date\" content=\"2018-11-20T19:00:00Z\" \/>\n<meta name=\"parsely-section\" content=\"NASA Centers & Facilities\" \/>\n<meta name=\"parsely-tags\" content=\"The Solar System,The Sun,Goddard Space Flight Center,Heliophysics,Heliophysics Division,RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager),Science Mission Directorate,Solar Flares,Space Weather\" \/>\n<meta name=\"parsely-author\" content=\"Abbey Interrante\" \/>","tracker_url":"https:\/\/cdn.parsely.com\/keys\/nasa.gov\/p.js"},"read_time":10,"time_ago":"6 years","featured_image":{"id":152570,"file":"https:\/\/www.nasa.gov\/wp-content\/uploads\/2018\/11\/rhessi.2018-11-20_09_49_32.gif","title":"rhessi.2018-11-20_09_49_32","alt":"animation of RHESSI satellite","caption":""},"_links":{"self":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/posts\/143333"}],"collection":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/users\/68"}],"replies":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/comments?post=143333"}],"version-history":[{"count":5,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/posts\/143333\/revisions"}],"predecessor-version":[{"id":304260,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/posts\/143333\/revisions\/304260"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/media\/152570"}],"wp:attachment":[{"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/media?parent=143333"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/categories?post=143333"},{"taxonomy":"news-tags","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/news-tags?post=143333"},{"taxonomy":"internal-terms","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/internal-terms?post=143333"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.nasa.gov\/wp-json\/wp\/v2\/coauthors?post=143333"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}