In celebration of the 20th anniversary of the first confirmed planet around a sun-like star, more than 60 leaders in the field of exoplanet observations chose their favorites among the nearly 2,000 known exoplanets. Some of the exoplanets are rocky, some are gaseous, and some are very, very odd. But there’s one thing each one of these strange new worlds has in common: All have advanced scientific understanding of our place in the cosmos.
Check out the astronomers’ top 10 list of exoplanets below, along with artist’s concepts depicting what they might look like.
Kepler-186f was the first rocky planet to be found within the habitable zone — the region around the host star where the temperature is right for liquid water. This planet is also very close in size to Earth. Even though we may not find out what’s going on at the surface of this planet anytime soon, it’s a strong reminder of why new technologies are being developed that will enable scientists to get a closer look at distant worlds.
Credits: NASA Ames/SETI Institute/JPL-Caltech
NASA Exoplanet Archive catalog page
2. HD 209458 b (nickname “Osiris”)
The first planet to be seen in transit (crossing its star) and the first planet to have it light directly detected. The HD 209458 b transit discovery showed that transit observations were feasible and opened up an entire new realm of exoplanet characterization.
Credits: NASA, European Space Agency, Alfred Vidal-Madjar (Institut d’Astrophysique de Paris, CNRS)
3. Kepler-11 system
This was the first compact solar system discovered by Kepler, and it revealed that a system can be tightly packed, with at least five planets within the orbit of Mercury, and still be stable. It touched off a whole new look into planet formation ideas and suggested that multiple small planet systems, like ours, may be common.
A real-life “Tatooine,” this planet was Kepler’s first discovery of a planet that orbits two stars — what is known as a circumbinary planet.
5. 51 Pegasi b
Scientists have reported the first conclusive discovery of water vapor in the atmosphere of an exoplanet, or a planet beyond our Solar System.
This artist’s impression shows a gas-giant exoplanet transiting across the face of its star. Infrared analysis by NASA’s Spitzer Space Telescope of this type of system provided the breakthrough.
The planet, HD 189733b, lies 63 light-years away in the constellation Vulpecula. It was discovered in 2005 as it transited its parent star, dimming the star’s light by some three percent.
This giant planet, which is about half the mass of Jupiter and orbits its star every four days, was the first confirmed exoplanet around a sun-like star, a discovery that launched a whole new field of exploration.
6. CoRoT 7b
The first super-Earth identified as a rocky exoplanet, this planet proved that worlds like the Earth were indeed possible and that the search for potentially habitable worlds (rocky planets in the habitable zone) might be fruitful.
Credits: ESO/L. Calçada
A planet in the habitable zone and a possible water-world planet unlike any seen in our solar system.
Kepler’s first rocky planet discovery is a scorched, Earth-size world that scientists believe may have a lava ocean on its surface.
Credits: NASA/Kepler Mission/Dana Berry
9. Kepler-444 system
The oldest known planetary system has five terrestrial-sized planets, all in orbital resonance. This weird group showed that solar systems have formed and lived in our galaxy for nearly its entire existence.
Credits: Tiago Campante/Peter Devine
10. 55 Cancri e
55 Cancri e is a toasty world that rushes around its star every 18 hours. It orbits so closely — about 25 times closer than Mercury is to our sun — that it is tidally locked with one face forever blisters under the heat of its sun. The planet is proposed to have a rocky core surrounded by a layer of water in a “supercritical” state, where it is both liquid and gas, and then the whole planet is thought to be topped by a blanket of steam.
Artist’s rendering of NASA’s Cassini spacecraft observing a sunset through Titan’s hazy atmosphere. Image credit: NASA/JPL-Caltech
Scientists working with data from NASA’s Cassini mission have developed a new way to understand the atmospheres of exoplanets by using Saturn’s smog-enshrouded moon Titan as a stand-in. The new technique shows the dramatic influence that hazy skies could have on our ability to learn about these alien worlds orbiting distant stars.
The work was performed by a team of researchers led by Tyler Robinson, a NASA Postdoctoral Research Fellow at NASA’s Ames Research Center in Moffett Field, California. The findings were published May 26 in the Proceedings of the National Academy of Sciences.
“It turns out there’s a lot you can learn from looking at a sunset,” Robinson said.
Light from sunsets, stars and planets can be separated into its component colors to create spectra, as prisms do with sunlight, in order to obtain hidden information. Despite the staggering distances to other planetary systems, in recent years researchers have begun to develop techniques for collecting spectra of exoplanets. When one of these worlds transits, or passes in front of its host star as seen from Earth, some of the star’s light travels through the exoplanet’s atmosphere, where it is changed in subtle, but measurable, ways. This process imprints information about the planet that can be collected by telescopes. The resulting spectra are a record of that imprint.
Spectra enable scientists to tease out details about what exoplanets are like, such as aspects of the temperature, composition and structure of their atmospheres.
Robinson and his colleagues exploited a similarity between exoplanet transits and sunsets witnessed by the Cassini spacecraft at Titan. These observations, called solar occultations, effectively allowed the scientists to observe Titan as a transiting exoplanet without having to leave the solar system. In the process, Titan’s sunsets revealed just how dramatic the effects of hazes can be.
Multiple worlds in our own solar system, including Titan, are blanketed by clouds and high-altitude hazes. Scientists expect that many exoplanets would be similarly obscured. Clouds and hazes create a variety of complicated effects that researchers must work to disentangle from the signature of these alien atmospheres, and thus present a major obstacle for understanding transit observations. Due to the complexity and computing power required to address hazes, models used to understand exoplanet spectra usually simplify their effects.
“Previously, it was unclear exactly how hazes were affecting observations of transiting exoplanets,” said Robinson. “So we turned to Titan, a hazy world in our own solar system that has been extensively studied by Cassini.”
The team used four observations of Titan made between 2006 and 2011 by Cassini’s visual and infrared mapping spectrometer instrument. Their analysis provided results that include the complex effects due to hazes, which can now be compared to exoplanet models and observations.
With Titan as their example, Robinson and colleagues found that hazes high above some transiting exoplanets might strictly limit what their spectra can reveal to planet transit observers. The observations might be able to glean information only from a planet’s upper atmosphere. On Titan, that corresponds to about 90 to 190 miles (150 to 300 kilometers) above the moon’s surface, high above the bulk of its dense and complex atmosphere.
An additional finding from the study is that Titan’s hazes more strongly affect shorter wavelengths, or bluer, colors of light. Studies of exoplanet spectra have commonly assumed that hazes would affect all colors of light in similar ways. Studying sunsets through Titan’s hazes has revealed that this is not the case.
“People had dreamed up rules for how planets would behave when seen in transit, but Titan didn’t get the memo,” said Mark Marley, a co-author of the study at NASA Ames. “It looks nothing like some of the previous suggestions, and it’s because of the haze.”
The team’s technique applies equally well to similar observations taken from orbit around any world, not just Titan. This means that researchers could study the atmospheres of planets like Mars and Saturn in the context of exoplanet atmospheres as well.
“It’s rewarding to see that Cassini’s study of the solar system is helping us to better understand other solar systems as well,” said Curt Niebur, Cassini program scientist at NASA Headquarters in Washington.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington. The VIMS team is based at the University of Arizona in Tucson.
More information about Cassini is available at the following sites:
The above story is based on materials provided by NASA/Jet Propulsion Laboratory. Note: Materials may be edited for content and length.
The University of Central Florida has detected what could be its first planet, only two-thirds the size of Earth and located right around the corner, cosmically speaking, at a mere 33light- years away.
The exoplanet candidate called UCF 1.01, is close to its star, so close it goes around the star in 1.4 days. The planet’s surface likely reaches temperatures of more than 1,000 degrees Fahrenheit. The discoverers believe that it has no atmosphere, is only two-thirds the gravity of Earth and that its surface may be volcanic or molten.”We have found strong evidence for a very small, very hot and very close-by planet with the help of the Spitzer Space Telescope,” said Kevin Stevenson, a recent PhD graduate from the UCF and lead author of the paper, which appears online tomorrow in The Astrophysical Journal. “This discovery is a significant accomplishment for UCF.”
Stevenson and his colleagues were studying a hot-Neptune exoplanet, designated GJ 436b, already known to exist around the red-dwarf star GJ 436, when data revealed clues that led them to suspect there could be at least one new planet in that system, perhaps two.
The team noticed slight dips in the amount of infrared light streaming from the star. A review of Spitzer archival data showed that the dips were periodic, suggesting that a planet might be blocking out a small fraction of light as it passed in front of GJ 436, as seen from Earth.
“I could see these faint dips in the starlight and I wanted to determine their source. I knew that if these signals were periodic, they could be from an unknown planet,” said Stevenson, who is now a postdoctoral scholar at the University of Chicago.
So he, UCF planetary sciences professor Joseph Harrington and UCF graduate student Nate Lust began looking at the data. They sifted through hundreds of hours of observations collected from Spitzer, the Deep Impact spacecraft, the ground-based Very Large Telescope in Chile and the Canada-France-Hawaii Telescope near the summit of Mauna Kea in Hawaii.
This transit technique, used by a number of telescopes, including NASA’s Kepler space telescope, relies on these tiny, partial eclipses to find exoplanet candidates.
Spitzer has performed science work on known exoplanets before, but UCF-1.01 represents the first time Spitzer has made a transit discovery.
With the finding of UCF-1.01, GJ 436 is likely now home to the first multi-transiting-planet system described by a mission other than Kepler. Of the 1,800 stars identified by Kepler as candidates for having planetary systems, only three are verified to contain sub-Earth size exoplanets.
The depth and duration of a transit reveals basic properties of an exoplanet, such as its size and distance from a host star. In UCF-1.01’s case, its diameter is estimated at 5,200 miles, or two-thirds that of Earth, placing the world among the smallest on record. The team also noticed hints of yet another potential planet dubbed UCF-1.02, but its period was impossible to estimate.
So why aren’t scientists calling UCF-1.01 a planet?
A measured mass is needed to verify that these objects are planets, but even the most sensitive instruments currently available are unable to measure exoplanet masses this small.
“Despite the lack of a confirmed mass, the team is confident future observations will verify our findings,” Harrington said.
Spitzer scientists are eager to see what the future will bring.
“I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars,” said Michael Werner, Spitzer Project Scientist at JPL. “Even after almost nine years in space, Spitzer’s observations continue to take us in new and important scientific directions.”
Credit: Artist’s Rendering provided by NASA