{"id":209130,"date":"2025-05-01T20:00:00","date_gmt":"2025-05-01T10:00:00","guid":{"rendered":"https:\/\/science.nasa.gov\/solar-system\/skywatching\/night-sky-network\/may2025-night-sky-notes\/"},"modified":"2025-05-01T20:00:00","modified_gmt":"2025-05-01T10:00:00","slug":"mays-night-sky-notes-how-do-we-find-exoplanets","status":"publish","type":"post","link":"https:\/\/www.vibewire.com.au\/?p=209130","title":{"rendered":"May\u2019s Night Sky Notes: How Do We Find Exoplanets?"},"content":{"rendered":"
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4 min read<\/p>\n

May\u2019s Night Sky Notes: How Do We Find Exoplanets?<\/h1>\n<\/div>\n<\/div>\n<\/div>\n

Astronomers have been trying to discover evidence that worlds exist around stars other than our Sun since the 19th century. By the mid-1990s, technology finally caught up with the desire for discovery and led to the first discovery of a planet orbiting another sun-like star,\u00a0Pegasi 51b<\/a>. Why did it take so long to discover these distant worlds, and what techniques do astronomers use to find them?<\/p>\n<\/p>\n

The Transit Method<\/h3>\n
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A planet passing in front of its parent star creates a drop in the star\u2019s apparent brightness, called a transit. Exoplanet Watch participants can look for transits in data from ground-based telescopes, helping scientists refine measurements of the length of a planet\u2019s orbit around its star.<\/div>\n
Credit: NASA\u2019s Ames Research Center<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n

One of the most famous exoplanet detection methods is the\u00a0transit method<\/strong>, used by\u00a0Kepler<\/a>\u00a0and other observatories. When a planet crosses in front of its host star, the light from the star dips slightly in brightness. Scientists can confirm a planet orbits its host star by repeatedly detecting these incredibly tiny dips in brightness using sensitive instruments. If you can imagine trying to detect the dip in light from a massive searchlight when an ant crosses in front of it, at a distance of tens of miles away, you can begin to see how difficult it can be to spot a planet from light-years away! Another drawback to the transit method is that the distant solar system must be at a favorable angle to our point of view here on Earth \u2013 if the distant system\u2019s angle is just slightly askew, there will be no transits. Even in our solar system, a transit is very rare. For example, there were two transits of Venus visible across our Sun from Earth in this century. But the next time Venus transits the Sun as seen from Earth will be in the year 2117 \u2013 more than a century from the 2012 transit, even though Venus will have completed nearly 150 orbits around the Sun by then!<\/p>\n

The Wobble Method<\/h3>\n
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As a planet orbits a star, the star wobbles. This causes a change in the appearance of the star\u2019s spectrum called Doppler shift. Because the change in wavelength is directly related to relative speed, astronomers can use Doppler shift to calculate exactly how fast an object is moving toward or away from us. Astronomers can also track the Doppler shift of a star over time to estimate the mass of the planet orbiting it.<\/div>\n
NASA, ESA, CSA, Leah Hustak (STScI)<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n

Spotting the Doppler shift of a star\u2019s spectra was used to find Pegasi 51b, the first planet detected around a Sun-like star.\u00a0This technique is called the\u00a0radial velocity or \u201cwobble\u201d method.\u00a0<\/strong>Astronomers split up the visible light emitted by a star into a rainbow. These spectra, and gaps between the normally smooth bands of light, help determine the elements that make up the star. However, if there is a planet orbiting the star, it causes the star to wobble ever so slightly back and forth. This will, in turn, cause the lines within the spectra to shift ever so slightly towards the blue and red ends of the spectrum as the star wobbles slightly away and towards us. This is caused by the\u00a0blue and red shifts<\/a>\u00a0of the star\u2019s light. By carefully measuring the amount of shift in the star\u2019s spectra, astronomers can determine the size of the object pulling on the host star and if the companion is indeed a planet. By tracking the variation in this periodic shift of the spectra, they can also determine the time it takes the planet to orbit its parent star.<\/p>\n

Direct Imaging<\/h3>\n

Finally, exoplanets can be revealed by\u00a0directly imaging<\/strong>\u00a0them, such as this image of four planets found orbiting the star HR 8799! Space telescopes use instruments called\u00a0coronagraphs<\/strong>\u00a0to block the bright light from the host star and capture the dim light from planets. The Hubble Space Telescope has\u00a0captured images of giant planets orbiting a few nearby systems<\/a>, and the James Webb Space Telescope\u00a0has only improved on these observations<\/a>\u00a0by uncovering more details, such as the colors and spectra of exoplanet atmospheres, temperatures, detecting potential exomoons, and even scanning atmospheres for potential biosignatures!<\/p>\n

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NASA\u2019s James Webb Space Telescope has provided the clearest look in the infrared yet at the iconic multi-planet system HR 8799. The closest planet to the star, HR 8799 e, orbits 1.5 billion miles from its star, which in our solar system would be located between the orbit of Saturn and Neptune. The furthest, HR 8799 b, orbits around 6.3 billion miles from the star, more than twice Neptune\u2019s orbital distance. Colors are applied to filters from Webb\u2019s NIRCam (Near-Infrared Camera), revealing their intrinsic differences. A star symbol marks the location of the host star HR 8799, whose light has been blocked by the coronagraph. In this image, the color blue is assigned to 4.1 micron light, green to 4.3 micron light, and red to the 4.6 micron light.<\/div>\n
NASA, ESA, CSA, STScI, W. Balmer (JHU), L. Pueyo (STScI), M. Perrin (STScI)<\/div>\n<\/figcaption><\/div>\n<\/div>\n<\/div>\n

You can find more information and activities on\u00a0NASA\u2019s Exoplanets<\/a>\u00a0page, such as the\u00a0Eyes on Exoplanets<\/a>\u00a0browser-based program,\u00a0The Exoplaneteers<\/a>, and some of the\u00a0latest exoplanet news<\/a>. Lastly, you can find more resources in our\u00a0News & Resources section<\/a>, including a\u00a0clever demo<\/a>\u00a0on how astronomers use the wobble method to detect planets!\u00a0<\/p>\n

The future of exoplanet discovery is only just beginning, promising rich rewards in humanity\u2019s understanding of our place in the Universe, where we are from, and if there is life elsewhere in our cosmos.<\/p>\n

Originally posted by Dave Prosper: July 2015
Last Updated by Kat Troche: April 2025<\/em><\/p><\/p>\n","protected":false},"excerpt":{"rendered":"

Astronomers have been trying to discover evidence that worlds exist around stars other than our Sun since the 19th century. By the mid-1990s, technology finally caught up with the desire for discovery and led to the first discovery of a planet orbiting another sun-like star,\u00a0Pegasi 51b. Why did it take so long to discover these [\u2026]<\/p>\n","protected":false},"author":24,"featured_media":1,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false,"footnotes":""},"categories":[15683],"tags":[],"class_list":["post-209130","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-night-sky-network"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/posts\/209130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=209130"}],"version-history":[{"count":2,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/posts\/209130\/revisions"}],"predecessor-version":[{"id":209351,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/wp\/v2\/posts\/209130\/revisions\/209351"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=\/"}],"wp:attachment":[{"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=209130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=209130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vibewire.com.au\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=209130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}