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NASA Telescope Reveals Largest Batch of Earth-Size, Habitable-Zone Planets Around Single Star

NASA’s Spitzer Space Telescope has revealed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water – key to life as we know it – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.”

At about 40 light-years (235 trillion miles) from Earth, the system of planets is relatively close to us, in the constellation Aquarius. Because they are located outside of our solar system, these planets are scientifically known as exoplanets.

This exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. In May 2016, researchers using TRAPPIST announced they had discovered three planets in the system. Assisted by several ground-based telescopes, including the European Southern Observatory’s Very Large Telescope, Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven.

The new results were published Wednesday in the journal Nature, and announced at a news briefing at NASA Headquarters in Washington.

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them, allowing their density to be estimated.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated – scientists believe it could be an icy, “snowball-like” world, but further observations are needed.

“The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star,” said Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium. “It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.”

In contrast to our sun, the TRAPPIST-1 star – classified as an ultra-cool dwarf – is so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun. The planets also are very close to each other. If a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of neighboring worlds, which would sometimes appear larger than the moon in Earth’s sky.

The planets may also be tidally locked to their star, which means the same side of the planet is always facing the star, therefore each side is either perpetual day or night. This could mean they have weather patterns totally unlike those on Earth, such as strong winds blowing from the day side to the night side, and extreme temperature changes.

Spitzer, an infrared telescope that trails Earth as it orbits the sun, was well-suited for studying TRAPPIST-1 because the star glows brightest in infrared light, whose wavelengths are longer than the eye can see. In the fall of 2016, Spitzer observed TRAPPIST-1 nearly continuously for 500 hours. Spitzer is uniquely positioned in its orbit to observe enough crossing – transits – of the planets in front of the host star to reveal the complex architecture of the system. Engineers optimized Spitzer’s ability to observe transiting planets during Spitzer’s “warm mission,” which began after the spacecraft’s coolant ran out as planned after the first five years of operations.

“This is the most exciting result I have seen in the 14 years of Spitzer operations,” said Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC in Pasadena, California. “Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets.”

Following up on the Spitzer discovery, NASA’s Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone. These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets.

In May 2016, the Hubble team observed the two innermost planets, and found no evidence for such puffy atmospheres. This strengthened the case that the planets closest to the star are rocky in nature.

“The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets,” said Nikole Lewis, co-leader of the Hubble study and astronomer at the Space Telescope Science Institute in Baltimore, Maryland. NASA’s planet-hunting Kepler space telescope also is studying the TRAPPIST-1 system, making measurements of the star’s minuscule changes in brightness due to transiting planets. Operating as the K2 mission, the spacecraft’s observations will allow astronomers to refine the properties of the known planets, as well as search for additional planets in the system. The K2 observations conclude in early March and will be made available on the public archive.

Spitzer, Hubble, and Kepler will help astronomers plan for follow-up studies using NASA’s upcoming James Webb Space Telescope, launching in 2018. With much greater sensitivity, Webb will be able to detect the chemical fingerprints of water, methane, oxygen, ozone, and other components of a planet’s atmosphere. Webb also will analyze planets’ temperatures and surface pressures – key factors in assessing their habitability.

NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate. Science operations are conducted at the Spitzer Science Center, at Caltech, in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at Caltech/IPAC. Caltech manages JPL for NASA.

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Source: NASA Solar SystemFelicia Chou / Sean Potter
Headquarters, Washington
202-358-1726 / 202-358-1536
felicia.chou@nasa.gov / sean.potter@nasa.gov

Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.

A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA's Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison.
Image Credit: NASA/ESA/STScI

NASA Telescopes Find Clear Skies and Water Vapor on Exoplanet

Astronomers using data from three of NASA’s space telescopes — Hubble, Spitzer and Kepler — have discovered clear skies and steamy water vapor on a gaseous planet outside our solar system. The planet is about the size of Neptune, making it the smallest planet from which molecules of any kind have been detected.

A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA's Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison. Image Credit: NASA/ESA/STScI
A plot of the transmission spectrum for exoplanet HAT-P-11b, with data from NASA’s Kepler, Hubble and Spitzer observatories combined. The results show a robust detection of water absorption in the Hubble data. Transmission spectra of selected atmospheric models are plotted for comparison.
Image Credit: NASA/ESA/STScI

“This discovery is a significant milepost on the road to eventually analyzing the atmospheric composition of smaller, rocky planets more like Earth,” said John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate in Washington. “Such achievements are only possible today with the combined capabilities of these unique and powerful observatories.”
Clouds in a planet’s atmosphere can block the view to underlying molecules that reveal information about the planet’s composition and history. Finding clear skies on a Neptune-size planet is a good sign that smaller planets might have similarly good visibility.
“When astronomers go observing at night with telescopes, they say ‘clear skies’ to mean good luck,” said Jonathan Fraine of the University of Maryland, College Park, lead author of a new study appearing in Nature. “In this case, we found clear skies on a distant planet. That’s lucky for us because it means clouds didn’t block our view of water molecules.”
The planet, HAT-P-11b, is categorized as an exo-Neptune — a Neptune-sized planet that orbits the star HAT-P-11. It is located 120 light-years away in the constellation Cygnus. This planet orbits closer to its star than does our Neptune, making one lap roughly every five days. It is a warm world thought to have a rocky core and gaseous atmosphere. Not much else was known about the composition of the planet, or other exo-Neptunes like it, until now.
Part of the challenge in analyzing the atmospheres of planets like this is their size. Larger Jupiter-like planets are easier to see because of their impressive girth and relatively inflated atmospheres. In fact, researchers already have detected water vapor in the atmospheres of those planets. The handful of smaller planets observed previously had proved more difficult to probe partially because they all appeared to be cloudy.
In the new study, astronomers set out to look at the atmosphere of HAT-P-11b, not knowing if its weather would call for clouds. They used Hubble’s Wide Field Camera 3, and a technique called transmission spectroscopy, in which a planet is observed as it crosses in front of its parent star. Starlight filters through the rim of the planet’s atmosphere; if molecules like water vapor are present, they absorb some of the starlight, leaving distinct signatures in the light that reaches our telescopes.
Using this strategy, Hubble was able to detect water vapor in HAT-P-11b. But before the team could celebrate clear skies on the exo-Neptune, they had to show that starspots — cooler “freckles” on the face of stars — were not the real sources of water vapor. Cool starspots on the parent star can contain water vapor that might erroneously appear to be from the planet.
The team turned to Kepler and Spitzer. Kepler had been observing one patch of sky for years, and HAT-P-11b happens to lie in the field. Those visible-light data were combined with targeted Spitzer observations taken at infrared wavelengths. By comparing these observations, the astronomers figured out that the starspots were too hot to have any steam. It was at that point the team could celebrate detecting water vapor on a world unlike any in our solar system. This discovery indicates the planet did not have clouds blocking the view, a hopeful sign that more cloudless planets can be located and analyzed in the future.
“We think that exo-Neptunes may have diverse compositions, which reflect their formation histories,” said study co-author Heather Knutson of the California Institute of Technology in Pasadena. “Now with data like these, we can begin to piece together a narrative for the origin of these distant worlds.”
The results from all three telescopes demonstrate that HAT-P-11b is blanketed in water vapor, hydrogen gas and likely other yet-to-be-identified molecules. Theorists will be drawing up new models to explain the planet’s makeup and origins.
“We are working our way down the line, from hot Jupiters to exo-Neptunes,” said Drake Deming, a co-author of the study also from University of Maryland. “We want to expand our knowledge to a diverse range of exoplanets.”
The astronomers plan to examine more exo-Neptunes in the future, and hope to apply the same method to super-Earths — massive, rocky cousins to our home world with up to 10 times the mass. Although our solar system doesn’t have a super-Earth, NASA’s Kepler mission is finding them in droves around other stars. NASA’s James Webb Space Telescope, scheduled to launch in 2018, will search super-Earths for signs of water vapor and other molecules; however, finding signs of oceans and potentially habitable worlds is likely a ways off.
“The work we are doing now is important for future studies of super-Earths and even smaller planets, because we want to be able to pick out in advance the planets with clear atmospheres that will let us detect molecules,” said Knutson.
Once again, astronomers will be crossing their fingers for clear skies.

Source: NASA