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By NASA
4 min read
May’s Night Sky Notes: How Do We Find Exoplanets?
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, Pegasi 51b. Why did it take so long to discover these distant worlds, and what techniques do astronomers use to find them?
The Transit Method
A planet passing in front of its parent star creates a drop in the star’s 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’s orbit around its star. Credit: NASA’s Ames Research Center One of the most famous exoplanet detection methods is the transit method, used by Kepler and 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 – if the distant system’s 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 – more than a century from the 2012 transit, even though Venus will have completed nearly 150 orbits around the Sun by then!
The Wobble Method
As a planet orbits a star, the star wobbles. This causes a change in the appearance of the star’s 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. NASA, ESA, CSA, Leah Hustak (STScI) Spotting the Doppler shift of a star’s spectra was used to find Pegasi 51b, the first planet detected around a Sun-like star. This technique is called the radial velocity or “wobble” method. 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 blue and red shifts of the star’s light. By carefully measuring the amount of shift in the star’s 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.
Direct Imaging
Finally, exoplanets can be revealed by directly imaging them, such as this image of four planets found orbiting the star HR 8799! Space telescopes use instruments called coronagraphs to block the bright light from the host star and capture the dim light from planets. The Hubble Space Telescope has captured images of giant planets orbiting a few nearby systems, and the James Webb Space Telescope has only improved on these observations by uncovering more details, such as the colors and spectra of exoplanet atmospheres, temperatures, detecting potential exomoons, and even scanning atmospheres for potential biosignatures!
NASA’s 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’s orbital distance. Colors are applied to filters from Webb’s 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. NASA, ESA, CSA, STScI, W. Balmer (JHU), L. Pueyo (STScI), M. Perrin (STScI) You can find more information and activities on NASA’s Exoplanets page, such as the Eyes on Exoplanets browser-based program, The Exoplaneteers, and some of the latest exoplanet news. Lastly, you can find more resources in our News & Resources section, including a clever demo on how astronomers use the wobble method to detect planets!
The future of exoplanet discovery is only just beginning, promising rich rewards in humanity’s understanding of our place in the Universe, where we are from, and if there is life elsewhere in our cosmos.
Originally posted by Dave Prosper: July 2015
Last Updated by Kat Troche: April 2025
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The NASA History Office brings you the new Spring 2025 issue of NASA History News & Notes reflecting on some of the transitional periods in NASA’s history, as well as the legacies of past programs. Topics include NASA’s 1967 class of astronauts, historic experiments in airborne astronomy, NASA’s aircraft consolidation efforts in the 1990s, lightning observations from space, the founding of the NACA, the DC-8 airborne science laboratory, and more!
Volume 42, Number 1
Spring 2025
Featured Articles
From the Chief Historian
By Brian Odom
In the first few months of 2025, NASA will celebrate several significant anniversaries, including the 110th anniversary of the National Advisory Committee for Aeronautics (NACA) (March 3), the 55th anniversary of the launch of Apollo 13 (April 11), and the 35th anniversary of the launch of the Hubble Space Telescope (April 24). Celebrating these important milestones is a way for us as an agency and for the public to reflect upon where we have been and what we have accomplished and to think about what we might accomplish next. Continue Reading
The XS-11 and the Transition Away from Mandatory Jet Pilot Training for NASA Astronauts
By Jennifer Ross-Nazzal
Flying in space has been associated with pilots ever since 1959, when NASA announced its first class of astronauts, known as the Mercury 7. Part of being a professional astronaut meant you were a certified jet pilot. Even the scientist-astronauts, so named to differentiate them from the astronauts assigned to the Mercury and Gemini missions, selected in 1965 and in 1967, received pilot training. Until NASA better understood the impact of weightlessness on the human body, Robert R. Gilruth, head of the Manned Spacecraft Center (MSC) in Houston, believed all astronauts should meet this qualification. But when five scientist-astronauts from the 1967 class had a rocky transition, leading them to resign—due to their disinterest in flying at the cost of their scientific training and no spaceflight opportunities—it eventually led NASA to rethink their idea of having all astronauts become jet pilots. Continue Reading
Portrait of NASA’s 1967 group of astronauts. Seated at the table, left to right, are Philip K. Chapman, Robert A. R. Parker, William E. Thornton, and John A. Llewellyn. Standing, left to right, are Joseph P. Allen IV, Karl G. Henize, Anthony W. England, Donald L. Holmquest, Story Musgrave, William B. Lenoir, and Brian T. O’Leary.NASA The High-Flying Legacy of Airborne Observation: How Experimental Aircraft Contributed to Astronomy at NASA
By Lois Rosson
In June 2011, the Stratospheric Observatory for Infrared Astronomy (SOFIA) chased down Pluto’s occultation of a far-away star. … SOFIA’s 2011 observation of Pluto followed up on a historic 1988 observation made by the airborne Kuiper Airborne Observatory (KAO) that proved that Pluto had an atmosphere at all. The technical versatility of both flights, conducted from aircraft hurtling stabilized telescopes through the air, speaks to the legacy of airborne astronomical observation at NASA. But how did this idiosyncratic format emerge in the first place? Airborne astronomy, in which astronomical observations are made from a moving aircraft, was attempted almost as soon as airplanes themselves were developed. Continue Reading
NASA’s Tortuous Effort to Consolidate its Aircraft
By Robert Arrighi
Thirty years ago, on January 6, 1995, NASA Administrator Dan Goldin announced, “We’ve started a revolution at NASA. It’s real. We have a road map for change. We’ve already begun.” Thus began one of the agency’s most daunting endeavors, a top-to-bottom reassessment of NASA’s processes, programmatic assignments, and staffing levels. One of the most controversial aspects of this effort was the proposal to transfer nearly all of the agency’s research aircraft to Dryden Flight Research Center (today known as Armstrong). Continue Reading
Three ER-2 Aircraft in formation over Golden Gate Bridge, San Francisco, CA on their final flight out of NASA Ames Research Center before redeployment to NASA’s Dryden Flight Research Center, now known as NASA Armstrong.NASA/Eric James The Space Between: Mesoscale Lightning Observations and Weather Forecasting, 1965–82
By Brad Massey
Skylab astronaut Edward G. Gibson looked down at Earth often during his 84 days on NASA’s first space station. From his orbital vantage point, Gibson took in the breathtaking views of our planet’s diverse landscapes. He also noted the interesting behavior of the planet’s most powerful electrical force: lightning. … Gibson’s words were of great interest to the lightning researchers affiliated with NASA’s Severe Storms and Local Research Program and others who believed observing Earth’s lightning from low Earth orbit generated valuable data that meteorologists could use to better forecast dangerous storm characteristics and behavior. With these motivations in mind, researchers created new Earth- and space-based experiments from the mid-1960s to the first Space Shuttle missions in the early 1980s that observed lightning on a regional level. Continue Reading
Adding Color to the Moon: Jack Kinzler’s Oral History Interviews
By Sandra Johnson
Manned Spacecraft Center (MSC) Director Robert R. Gilruth placed a call to Jack Kinzler less than four months before the Apollo 11 launch. Gilruth asked him to attend a meeting with a high-level group of individuals from both MSC and NASA Headquarters to discuss ideas for celebrating the first lunar landing. Kinzler, in his capacity as the chief of the Technical Services Division, arrived ready to present his suggestions for commemorating the achievement. Continue Reading
Apollo 11 astronaut Edwin E. “Buzz” Aldrin Jr. poses for a photograph beside the deployed United States flag during the mission’s extravehicular activity (EVA) on the lunar surface.NASA The Founding of the NACA
By James Anderson
One hundred ten years ago this month, NASA’s predecessor organization, the National Advisory Committee for Aeronautics (NACA), was founded. The date of the anniversary marks the passage of a rider to a naval appropriations bill that established the NACA for the modest sum of $5,000 annually. Telling the story of the NACA’s founding in this manner—using March 3, 1915, as the moment in time to represent the NACA’s beginning—is true, but it overlooks two crucial aspects of the founding. The founding was both a culmination and a turning point for science and aeronautics in the United States. Continue Reading
Remembering the DC-8 Airborne Science Laboratory at NASA
By Bradley Lynn Coleman
The NASA History Office and NASA Earth Science Division cohosted a workshop on the recently retired NASA DC-8 Airborne Science Laboratory (1986–2024) at the Mary W. Jackson NASA Headquarters Building in Washington, DC, October 24 and 25, 2024. The workshop celebrated the history of the legendary aircraft; documented DC-8–enabled scientific, engineering, education, and outreach activities; and captured lessons of the past for future operators. Continue Reading
The DC-8 in flight near Lone Pine, California. NASA/Jim Ross Download the Spring 2025 Edition More Issues of NASA History News and Notes Share
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