Astronomers Look at Super-Earths That had Their Atmospheres Stripped Away by Their Stars

As the planets of our Solar System demonstrate, understanding the solar dynamics of a system is a crucial aspect of determining habitability. Because of its protective magnetic field, Earth has maintained a fluffy atmosphere for billions of years, ensuring a stable climate for life to evolve. In contrast, other rocky planets that orbit our Sun are either airless, have super-dense (Venus), or have very thin atmospheres (Mars) due to their interactions with the Sun.

In recent years, astronomers have been on the lookout for this same process when studying extrasolar planets. For instance, an international team of astronomers led by the National Astronomical Observatory of Japan (NAOJ) recently conducted follow-up observations of two Super-Earths that orbit very closely to their respective stars. These planets, which have no thick primordial atmospheres, represent a chance to investigate the evolution of atmospheres on hot rocky planets.

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Larger Rocky Planets Might be Rare Because They Shrunk

Researchers at the Flatiron Institute’s Center for Computational Astrophysics published a paper last week that just might explain a mysterious gap in planet sizes beyond our solar system. Planets between 1.5 and 2 times Earth’s radius are strikingly rare. This new research suggests that the reason might be because planets slightly larger than this, called mini-Neptunes, lose their atmospheres over time, shrinking to become ‘super-Earths’ only slightly larger than our home planet. These changing planets only briefly have a radius the right size to fill the gap, quickly shrinking beyond it. The implication for planetary science is exciting, as it affirms that planets are not static objects, but evolving and dynamic worlds.

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What Are Extrasolar Planets?

For countless generations, human beings have looked out at the night sky and wondered if they were alone in the Universe. With the discovery of other planets in our Solar System, the true extent of the Milky Way galaxy, and other galaxies beyond our own, this question has only deepened and become more profound.

And whereas astronomers and scientists have long suspected that other star systems in our galaxy and the Universe had orbiting planets of their own, it has only been within the last few decades that any have been observed. Over time, the methods for detecting these “extrasolar planets” have improved, and the list of those whose existence has been confirmed has grown accordingly (over 4000 and counting!)

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One of the Oldest Stars in the Galaxy has a Planet. Rocky Planets Were Forming at Nearly the Beginning of the Universe

Would it be surprising to find a rocky planet that dates back to the very early Universe? It should be. The early Universe lacked the heavier elements necessary to form rocky planets.

But astronomers have found one, right here in the Milky Way.

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TESS Has Now Captured Almost the Entire Southern Sky. Here’s a Mosaic Made of 15,347 Photographs

On April 18th, 2018, NASA’s Transitting Exoplanet Survey Satellite (TESS) took to space for the first time. By August, it began capturing the light curves of distant stars for signs of planetary transits, effectively picking up where the Kepler Space Telescope left off. Now, just a few months away from the end of its primary mission, NASA has put a year’s worth of images of the southern sky together to create the beautiful mosaic you see here.

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NASA Promised More Smaller, Earth-size Exoplanets. TESS is Delivering.

When NASA launched TESS (Transiting Exoplanet Survey Satellite) in 2018, it had a specific goal. While its predecessor, the Kepler spacecraft, found thousands of exoplanets, many of them were massive gas giants. TESS was sent into space with a promise: to find smaller planets similar in size to Earth and Neptune, orbiting stable stars without much flaring. Those constraints, astronomers hoped, would identify more exoplanets that are potentially habitable.

With this discovery of three new exoplanets, TESS is fulfilling its promise.

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TESS Just Found its First Earth-Sized World

Artist's conception of HD 21749c, the first Earth-sized planet found by NASA's Transiting Exoplanets Survey Satellite (TESS), as well as its sibling, HD 21749b, a warm sub-Neptune-sized world. Credit: Robin Dienel/Carnegie Institution for Science.

NASA’s new planet-hunting telescope, TESS (Transiting Exoplanet Survey Satellite), just found its first Earth-sized world. Though the Earth-sized planet, and its hot sub-Neptune companion, were first observed by TESS in January 2019, it’s taken until now to confirm their status with ground-based follow-up observations. The discovery is published in The Astrophysical Journal Letters.

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Now that TESS is Operational, Astronomers Estimate it’ll Find 14,000 Planets. 10 Could Be Earthlike Worlds in a Sunlike Star’s Habitable Zone

An artist’s illustration of the Transiting Exoplanet Survey Satellite. Credits: NASA Goddard Space Flight Center

How many exoplanets are there? Not that long ago, we didn’t know if there were any. Then we detected a few around pulsars. Then the Kepler spacecraft was launched and it discovered a couple thousand more. Now NASA’s TESS (Transiting Exoplanet Survey Satellite) is operational, and a new study predicts its findings.

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It’s Over For Kepler. The Most Successful Planet Hunter Ever Built is Finally out of Fuel and Has Just Been Shut Down.

NASA's Kepler space telescope, shown in this artist's concept, revealed that there are more planets than stars in the Milky Way galaxy. Credit: NASA

It’s been quite a tumultuous time for space telescopes lately! Less than a month ago, the Hubble Space Telescope went into safe mode after experiencing a mechanical failure with one of its gyroscopes (which has since been remedied). Shortly thereafter, the Chandra X-ray telescope went into safe mode as well, and for similar reasons. After three days, it’s operations team managed to get it back in working order as well.

And now, after nine years of service, NASA has officially announced that the Kepler Space Telescope will be retiring. With no fuel remaining to conduct its science observations, NASA has decided to leave the telescope in its current safe orbit (well away from Earth). Far from being a sad occasion, Kepler’s retirement is an opportunity to reflect upon the immense accomplishments of this telescope and how it revolutionized the study of exoplanets.

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TESS Practices on a Comet Before Starting on its Science Operations

An artist’s illustration of the Transiting Exoplanet Survey Satellite. Credits: NASA Goddard Space Flight Center

On April 18th, 2018, NASA deployed the Transiting Exoplanet Survey Satellite (TESS), a next-generation exoplanet hunting telescope that is expected to find thousands of planets in the coming years. Alongside other next-generation telescopes like the James Webb Space Telescope (JWST), TESS will effectively pick up where space telescopes like Hubble and Kepler left off.

The mission recently started science operations (on July 25th, 2018) and is expected to transmit its first collection of data back to Earth this month. But before that, the planet-hunting telescope took a series of images that featured a recently-discovered comet known as C/2018 N1. These images helped demonstrate the satellite’s ability to collect images over a broad region of the sky – which will be critical when it comes to finding exoplanets.

As the name would suggest, the TESS mission is designed to search for planets around distant stars using the Transit Method (aka. Transit Photometry). For this method, distant stars are monitored for periodic dips in brightness, which are indications that a planet is passing in front of the star (aka. transiting) relative to the observer. From these dips, astronomers are able to estimate a planet’s size and orbital period.

This method remains the most effective and popular means for finding exoplanets, accounting for 2,951 of the 3,774 confirmed discoveries made to date. To test its instruments before it began science operations, TESS took images of C/2018 N1 over a short period near the end of the mission’s commissioning phase – which occurred over the course of 17 hours on July 25th.

The comet that it managed to capture, C/2018 N1, was discovered by NASA’s Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) satellite on June 29th. This comet is located about 48 million km (29 million mi) from Earth in the southern constellation Piscis Austrinus. In these pictures, which were compiled into a video (shown below), the comet is seen as a bright dot against a background of stars and other objects.

As it moves across the frame (from right to left), the comet’s tail can be seen extending to the top of the frame, and gradually changes direction as the comet glides across the field of view. The images also reveal a considerable amount of astronomical activity in the background. For instance, image processing causes the stars to shift between white and black, which highlights some variable stars visible in the images.

These are stars that change brightness as a result of pulsation, rapid rotation, or being eclipsed by a binary neighbor. A number of Solar System asteroids are also visible as small white dots moving across the field of view. Last, but not least, some stray light that was reflected from Mars is also visible near the end of the video. This light appears as a faint broad arc that moves across the middle section of the frame, from left to right.

This effect was due to the fact that Mars was at its brightest at the time since it was near opposition (i.e. at the closest point in its orbit to Earth). These images showcase the capabilities of the TESS mission, even though they only show a fraction of the instrument’s active field of view.

In the coming weeks and months, TESS science team will continue to fine-tune the spacecraft’s performance as it searches for extra-solar planets. As noted, it is expected that TESS will find thousands of planets in our galaxy, vastly increasing our knowledge of exoplanets and the kinds of worlds that exist beyond our Solar System!

And be sure to check out the video of the images TESS captured, courtesy of NASA’s Goddard Space Flight Center:

Further Reading: NASA