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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
2 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
https://youtu.be/63uNNcCpxHI How are we made of star stuff?
Well, the important thing to understand about this question is that it’s not an analogy, it’s literally true.
The elements in our bodies, the elements that make up our bones, the trees we see outside, the other planets in the solar system, other stars in the galaxy. These were all part of stars that existed well before our Sun and Earth and solar system were even formed.
The universe existed for billions of years before we did. And all of these elements that you see on the periodic table, you see carbon and oxygen and silicon and iron, the common elements throughout the universe, were all put there by previous generations of stars that either blew off winds like the Sun blows off a solar wind, or exploded in supernova explosions and thrust their elements throughout the universe.
These are the same things that we can trace with modern telescopes, like the Hubble Telescope and the James Webb Space Telescope, the Chandra X-ray Observatory. These are all elements that we can map out in the universe with these observatories and trace back to the same things that form us and the elemental abundances that we see in stars now are the same things that we see in the Earth’s crust, we see in asteroids. And so we know that these are the same elements that were once part of these stars.
So the question of, “How are we made of star stuff?”, in the words of Carl Sagan, “The cosmos is within us. We are made of star stuff. We are a way for the universe to know itself.”
[END VIDEO TRANSCRIPT]
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Last Updated Apr 28, 2025 Related Terms
General Astrophysics Astrophysics Division Chandra X-Ray Observatory Hubble Space Telescope James Webb Space Telescope (JWST) Origin & Evolution of the Universe Science Mission Directorate The Solar System The Universe Explore More
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By NASA
NASA’s James Webb Space Telescope has taken the most detailed image of planetary nebula NGC 1514 to date thanks to its unique mid-infrared observations. Webb shows its rings as intricate clumps of dust. It’s also easier to see holes punched through the bright pink central region.NASA, ESA, CSA, STScI, Michael Ressler (NASA-JPL), Dave Jones (IAC) In this photo released on April 14, 2025, NASA’s James Webb Space Telescope revealed the gas and dust ejected by a dying star at the heart of NGC 1514. Using mid-infrared data showed the “fuzzy” clumps arranged in tangled patterns, and a network of clearer holes close to the central stars shows where faster material punched through.
This scene has been forming for at least 4,000 years — and will continue to change over many more millennia. At the center are two stars that appear as one in Webb’s observation, and are set off with brilliant diffraction spikes. The stars follow a tight, elongated nine-year orbit and are draped in an arc of dust represented in orange.
One of these stars, which used to be several times more massive than our Sun, took the lead role in producing this scene. “As it evolved, it puffed up, throwing off layers of gas and dust in in a very slow, dense stellar wind,” said David Jones, a senior scientist at the Institute of Astrophysics on the Canary Islands, who proved there is a binary star system at the center in 2017.
Learn more about planetary nebula NGC 1514.
Image credit: NASA, ESA, CSA, STScI, Michael Ressler (NASA-JPL), Dave Jones (IAC)
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By European Space Agency
Each year, cutting-edge technologies developed by the European Space Agency (ESA) for its complex missions and scientific discoveries find new life in applications used to benefit Earth and improve our daily lives.
From 9–13 April, ESA was guest of honour at the 50th International Exhibition of Inventions Geneva in Switzerland with more than 1000 inventions, which attracted 30 000 visitors from the public. ESA showcased its new technologies and applications that have been invented for space missions and patented for use in and outside the space arena.
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