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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 European Space Agency
This new snapshot from the European Space Agency’s Mars Express deftly captures the two distinct faces of Mars: ridged and rugged versus smooth and unmarked.
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By NASA
5 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
A Martian dust devil can be seen consuming its smaller friend in this short video made of images taken at the rim of Jezero Crater by NASA’s Perseverance Mars rover on Jan. 25, 2025. NASA/JPL-Caltech/SSI The six-wheeled explorer recently captured several Red Planet mini-twisters spinning on the rim of Jezero Crater.
A Martian dust devil can be seen consuming a smaller one in this short video made of images taken by a navigation camera aboard NASA’s Perseverance Mars rover. These swirling, sometimes towering columns of air and dust are common on Mars. The smaller dust devil’s demise was captured during an imaging experiment conducted by Perseverance’s science team to better understand the forces at play in the Martian atmosphere.
When the rover snapped these images from about 0.6 miles (1 kilometer) away, the larger dust devil was approximately 210 feet (65 meters) wide, while the smaller, trailing dust devil was roughly 16 feet (5 meters) wide. Two other dust devils can also be seen in the background at left and center. Perseverance recorded the scene Jan. 25 as it explored the western rim of Mars’ Jezero Crater at a location called “Witch Hazel Hill.”
“Convective vortices — aka dust devils — can be rather fiendish,” said Mark Lemmon, a Perseverance scientist at the Space Science Institute in Boulder, Colorado. “These mini-twisters wander the surface of Mars, picking up dust as they go and lowering the visibility in their immediate area. If two dust devils happen upon each other, they can either obliterate one another or merge, with the stronger one consuming the weaker.”
While exploring the rim of Jezero Crater on Mars, NASA’s Perseverance rover captured new images of multiple dust devils in January 2025. These captivating phenomena have been documented for decades by the agency’s Red Planet robotic explorers. NASA/JPL-Caltech/LANL/CNES/CNRS/INTA-CSIC/Space Science Institute/ISAE-Supaero/University of Arizona Science of Whirlwinds
Dust devils are formed by rising and rotating columns of warm air. Air near the planet’s surface becomes heated by contact with the warmer ground and rises through the denser, cooler air above. As other air moves along the surface to take the place of the rising warmer air, it begins to rotate. When the incoming air rises into the column, it picks up speed like a spinning ice skater bringing their arms closer to their body. The air rushing in also picks up dust, and a dust devil is born.
“Dust devils play a significant role in Martian weather patterns,” said Katie Stack Morgan, project scientist for the Perseverance rover at NASA’s Jet Propulsion Laboratory in Southern California. “Dust devil study is important because these phenomena indicate atmospheric conditions, such as prevailing wind directions and speed, and are responsible for about half the dust in the Martian atmosphere.”
NASA’s Viking 1 orbiter captured this Martian dust devil casting a shadow on Aug. 1, 1978. During the 15-second interval between the two images, the dust devil moved toward the northeast (toward the upper right) at a rate of about 59 feet (18 meters) per second. NASA/JPL-Caltech/MSSS Since landing in 2021, Perseverance has imaged whirlwinds on many occasions, including one on Sept. 27, 2021, where a swarm of dust devils danced across the floor of Jezero Crater and the rover used its SuperCam microphone to record the first sounds of a Martian dust devil.
NASA’s Viking orbiters, in the 1970s, were the first spacecraft to photograph Martian dust devils. Two decades later, the agency’s Pathfinder mission was the first to image one from the surface and even detected a dust devil passing over the lander. Twin rovers Spirit and Opportunity managed to capture their fair share of dusty whirlwinds. Curiosity, which is exploring a location called Mount Sharp in Gale Crater on the opposite side of the Red Planet as Perseverance, sees them as well.
Capturing a dust devil image or video with a spacecraft takes some luck. Scientists can’t predict when they’ll appear, so Perseverance routinely monitors in all directions for them. When scientists see them occur more frequently at a specific time of day or approach from a certain direction, they use that information to focus their monitoring to try to catch additional whirlwinds.
“If you feel bad for the little devil in our latest video, it may give you some solace to know the larger perpetrator most likely met its own end a few minutes later,” said Lemmon. “Dust devils on Mars only last about 10 minutes.”
More About Perseverance
A key objective of Perseverance’s mission on Mars is astrobiology, including caching samples that may contain signs of ancient microbial life. The rover is characterizing the planet’s geology and past climate, to help pave the way for human exploration of the Red Planet and as the first mission to collect and cache Martian rock and regolith.
NASA’s Mars Sample Return Program, in cooperation with ESA (European Space Agency), is designed to send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis.
The Mars 2020 Perseverance mission is part of NASA’s Mars Exploration Program (MEP) portfolio and the agency’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.
NASA’s Jet Propulsion Laboratory, which is managed for the agency by Caltech, built and manages operations of the Perseverance rover.
For more about Perseverance:
https://science.nasa.gov/mission/mars-2020-perseverance
News Media Contacts
DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov
Karen Fox / Molly Wasser
NASA Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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Last Updated Apr 03, 2025 Related Terms
Perseverance (Rover) Curiosity (Rover) Jet Propulsion Laboratory Mars Mars 2020 Mars Exploration Rovers (MER) Mars Pathfinder Viking Explore More
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By NASA
3 Min Read March’s Night Sky Notes: Messier Madness
Showing a large portion of M66, this Hubble photo is a composite of images obtained at visible and infrared wavelengths. The images have been combined to represent the real colors of the galaxy. Credits:
NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration; Acknowledgment: Davide De Martin and Robert Gendler by Kat Troche of the Astronomical Society of the Pacific
What Are Messier Objects?
During the 18th century, astronomer and comet hunter Charles Messier wanted to distinguish the ‘faint fuzzies’ he observed from any potential new comets. As a result, Messier cataloged 110 objects in the night sky, ranging from star clusters to galaxies to nebulae. These items are designated by the letter ‘M’ and a number. For example, the Orion Nebula is Messier 42 or M42, and the Pleiades are Messier 45 or M45. These are among the brightest ‘faint fuzzies’ we can see with modest backyard telescopes and some even with our eyes.
Stargazers can catalog these items on evenings closest to the new moon. Some even go as far as having “Messier Marathons,” setting up their telescopes and binoculars in the darkest skies available to them, from sundown to sunrise, to catch as many as possible. Here are some items to look for this season:
M44 in Cancer and M65 and 66 in Leo can be seen high in the evening sky 60 minutes after sunset. Stellarium Web Messier 44 in Cancer: The Beehive Cluster, also known as Praesepe, is an open star cluster in the heart of the Cancer constellation. Use Pollux in Gemini and Regulus in Leo as guide stars. A pair of binoculars is enough to view this and other open star clusters. If you have a telescope handy, pay a visit two of the three galaxies that form the Leo Triplet – M65 and M66. These items can be seen one hour after sunset in dark skies.
Locate M3 and M87 rising in the east after midnight. Stellarium Web Messier 3 Canes Venatici: M3 is a globular cluster of 500,000 stars. Through a telescope, this object looks like a fuzzy sparkly ball. You can resolve this cluster in an 8-inch telescope in moderate dark skies. You can find this star cluster by using the star Arcturus in the Boötes constellation as a guide.
Messier 87 in Virgo: Located just outside of Markarian’s Chain, M87 is an elliptical galaxy that can be spotted during the late evening hours. While it is not possible to view the supermassive black hole at the core of this galaxy, you can see M87 and several other Messier-labeled galaxies in the Virgo Cluster using a medium-sized telescope.
Locate M76 and M31 setting in the west, 60 minutes after sunset. Stellarium Web Plan Ahead
When gearing up for a long stargazing session, there are several things to remember, such as equipment, location, and provisions:
Do you have enough layers to be outdoors for several hours? You would be surprised how cold it can get when sitting or standing still behind a telescope! Are your batteries fully charged? If your telescope runs on power, be sure to charge everything before you leave home and pack any additional batteries for your cell phone. Most people use their mobile devices for astronomy apps, so their batteries may deplete faster. Cold weather can also impact battery life. Determine the apparent magnitude of what you are trying to see and the limiting magnitude of your night sky. You can learn more about apparent and limiting magnitudes with our Check Your Sky Quality with Orion article. When choosing a location to observe from, select an area you are familiar with and bring some friends! You can also connect with your local astronomy club to see if they are hosting any Messier Marathons. It’s always great to share the stars! You can see all 110 items and their locations with NASA’s Explore the Night Sky interactive map and the Hubble Messier Catalog, objects that have been imaged by the Hubble Space Telescope.
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