NASA's Spitzer Sees the Light of Alien 'Super Earth'

NASA's Spitzer Space Telescope was able to detect a super Earth's direct light for the first time using its sensitive heat-seeking infrared vision. Super Earth's are more massive than Earth but lighter than gas giants like Neptune. As this artist's concept shows, in visible light, a planet is lost in the glare of its star (top view). When viewed in infrared, the planet becomes brighter relative to its star. This is largely due to the fact that the planet's scorching heat blazes with infrared light. Even on our own bodies emanate more infrared light than visible due to our heat. Image credit: NASA/JPL-Caltech. Full image and caption

This plot of data from NASA's Spitzer Space Telescope reveals the light from a "super Earth" called 55 Cancri e. The planet is the smallest yet, beyond our solar system, to reveal its direct light. Super Earth's are more massive than Earth but lighter than gas giants like Neptune. While this planet is not habitable, the observations are an important milestone toward being able to eventually perform a similar technique on even smaller, potentially Earth-like planets. Image credit: NASA/JPL-Caltech/MIT. Full image and caption - enlarge image

Super Earth Reveals Itself to Spitzer

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PASADENA, Calif. - NASA's Spitzer Space Telescope has detected light emanating from a "super-Earth" planet beyond our solar system for the first time. While the planet is not habitable, the detection is a historic step toward the eventual search for signs of life on other planets.

"Spitzer has amazed us yet again," said Bill Danchi, Spitzer program scientist at NASA Headquarters in Washington. "The spacecraft is pioneering the study of atmospheres of distant planets and paving the way for NASA's upcoming James Webb Space Telescope to apply a similar technique on potentially habitable planets."

The planet, called 55 Cancri e, falls into a class of planets termed super Earths, which are more massive than our home world but lighter than giant planets like Neptune. The planet is about twice as big and eight times as massive as Earth. It orbits a bright star, called 55 Cancri, in a mere 18 hours.

Previously, Spitzer and other telescopes were able to study the planet by analyzing how the light from 55 Cancri changed as the planet passed in front of the star. In the new study, Spitzer measured how much infrared light comes from the planet itself. The results reveal the planet is likely dark, and its sun-facing side is more than 2,000 Kelvin (3,140 degrees Fahrenheit), hot enough to melt metal.

The new information is consistent with a prior theory that 55 Cancri e is a water world: a rocky core surrounded by a layer of water in a "supercritical" state where it is both liquid and gas, and topped by a blanket of steam.

"It could be very similar to Neptune, if you pulled Neptune in toward our sun and watched its atmosphere boil away," said Michaël Gillon of Université de Liège in Belgium, principal investigator of the research, which appears in the Astrophysical Journal. The lead author is Brice-Olivier Demory of the Massachusetts Institute of Technology in Cambridge.

The 55 Cancri system is relatively close to Earth, at 41 light-years away. It has five planets, with 55 Cancri e the closest to the star and tidally locked, so one side always faces the star. Spitzer discovered the sun-facing side is extremely hot, indicating the planet probably does not have a substantial atmosphere to carry the sun's heat to the unlit side.

NASA's James Webb Space Telescope, scheduled to launch in 2018, likely will be able to learn even more about the planet's composition. The telescope might be able to use a similar infrared method to Spitzer to search other potentially habitable planets for signs of molecules possibly related to life.

"When we conceived of Spitzer more than 40 years ago, exoplanets hadn't even been discovered," said Michael Werner, Spitzer project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Because Spitzer was built very well, it's been able to adapt to this new field and make historic advances such as this."

In 2005, Spitzer became the first telescope to detect light from a planet beyond our solar system. To the surprise of many, the observatory saw the infrared light of a "hot Jupiter," a gaseous planet much larger than the solid 55 Cancri e. Since then, other telescopes, including NASA's Hubble and Kepler space telescopes, have performed similar feats with gas giants using the same method.

In this method, a telescope gazes at a star as a planet circles behind it. When the planet disappears from view, the light from the star system dips ever so slightly, but enough that astronomers can determine how much light came from the planet itself. This information reveals the temperature of a planet, and, in some cases, its atmospheric components. Most other current planet-hunting methods obtain indirect measurements of a planet by observing its effects on the star.

During Spitzer's ongoing extended mission, steps were taken to enhance its unique ability to see exoplanets, including 55 Cancri e. Those steps, which included changing the cycling of a heater and using an instrument in a new way, led to improvements in how precisely the telescope points at targets.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology (Caltech) in Pasadena. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit: http://www.nasa.gov/spitzer and http://spitzer.caltech.edu .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
Whitney.clavin@jpl.nasa.gov

J. D. Harrington 202-358-5241
NASA Headquarters, Washington
j.d.harrington@nasa.gov

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Re-thinking an Alien World

An artist's concept of Earth and 55 Cancri e
positioned side by side for comparison. [video]

Spitzer recently measured the extraordinarily small amount of light 55 Cancri e blocks when it crosses in front of its star. These transits occur every 18 hours, giving researchers repeated opportunities to gather the data they need to estimate the width, volume and density of the planet.

According to the new observations, 55 Cancri e has a mass 7.8 times and a radius just over twice that of Earth. Those properties place 55 Cancri e in the "super-Earth" class of exoplanets, a few dozen of which have been found. Only a handful of known super-Earths, however, cross the face of their stars as viewed from our vantage point in the cosmos, so 55 Cancri e is better understood than most.

When 55 Cancri e was discovered in 2004, initial estimates of its size and mass were consistent with a dense planet of solid rock. Spitzer data suggest otherwise: About a fifth of the planet's mass must be made of light elements and compounds--including water. Given the intense heat and high pressure these materials likely experience, researchers think the compounds likely exist in a "supercritical" fluid state.

A supercritical fluid is a high-pressure, high-temperature state of matter best described as a liquid-like gas, and a marvelous solvent. Water becomes supercritical in some steam turbines--and it tends to dissolve the tips of the turbine blades. Supercritical carbon dioxide is used to remove caffeine from coffee beans, and sometimes to dry-clean clothes. Liquid-fueled rocket propellant is also supercritical when it emerges from the tail of a spaceship.

On 55 Cancri e, this stuff may be literally oozing--or is it steaming?--out of the rocks.

With supercritical solvents rising from the planet’s surface, a star of terrifying proportions filling much of the daytime sky, and whole years rushing past in a matter of hours, 55 Cancri e teaches a valuable lesson: Just because a planet is similar in size to Earth does not mean the planet is like Earth.

It’s something to re-think about.

Author: Dr. Tony Phillips
Production editor: Dr. Tony Phillips

Credit: Science@NASA

More Information

Credits: The original research reported in this story has been accepted for publication in Astronomy and Astrophysics. The lead author is Brice-Olivier Demory, a post-doctoral associate in Professor Sara Seager's group at MIT.

Spitzer Space Telescope -- home page

Kepler Discovers a Tiny Solar System -- Science@NASA

Kepler Discovers Three "Hot Earths" -- Science@NASA

Kepler Confirms Exo-Planets in the "Goldilocks Zone" -- Science@NASA

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Spitzer Detects a Steaming Super-Earth Eclipsing Its Star

55 Cancri e
Credit: NASA/JPL-Caltech/R. Hurt (SSC)

NASA's Spitzer Space Telescope has gathered surprising new details about a supersized and superheated version of Earth called 55 Cancri e. According to Spitzer data, the exoplanet is less dense than previously thought, a finding which profoundly changes the portrait of this exotic world. Instead of a dense rock scorched dry by its sun, 55 Cancri e likely has water vapor and other gases steaming from its molten surface.

Spitzer measured the extraordinarily small amount of light 55 Cancri e blocked when the planet crossed in front of its star. These mini-eclipses, called transits, allow astronomers to accurately determine a planet's size and calculate its density. Promisingly, the results show how astronomers can use Spitzer, operating in "warm" mode since depleting its liquid coolant in May 2009, to probe the properties of strange alien worlds.

"This work demonstrates that 'warm' Spitzer can measure an extremely faint eclipse caused by exoplanets' transits with very high precision," said Brice-Olivier Demory, a post-doctoral associate in Professor Sara Seager's group in the Earth, Atmospheric and Planetary Sciences department at the Massachusetts Institute of Technology (MIT). Demory, who is lead author of a paper accepted for publication in Astronomy & Astrophysics, said that the study "emphasizes the important role Spitzer still has to play for the detection and characterization of transiting planets."

Blazing Hot and on the Move

Astronomers first discovered 55 Cancri e in 2004, and continued investigation of the exoplanet has shown it to be a truly bizarre place. The world revolves around its sunlike star in the shortest time period of all known exoplanets - just 17 hours and 40 minutes. (In other words, a year on 55 Cancri e lasts less than 18 hours.) The exoplanet orbits about 26 times closer to its star than Mercury, the most Sun-kissed planet in our solar system. Such proximity means that 55 Cancri e's surface roasts at a minimum of 3,200 degrees Fahrenheit (1,760 degrees Celsius).

The new observations with Spitzer reveal 55 Cancri e to have a mass 7.8 times and a radius just over twice that of Earth. Those properties place 55 Cancri e in the "super-Earth" class of exoplanets, a few dozen of which have been found. Only a handful of known super-Earths, however, cross the face of their stars as viewed from our vantage point in the cosmos. At just 40 light years away, 55 Cancri e stands as the smallest transiting super-Earth in our stellar neighborhood. In fact, 55 Cancri is so bright and close that it can be seen with the naked eye on a clear, dark night.

Based on the precise Spitzer data, Demory and his colleagues came up with a revised, lower density for 55 Cancri e. Coupled with its tight orbit, 55 Cancri e possesses a unique combination of super-Earth traits. Its low density is similar to that of a cooler super-Earth called GJ1214b, discovered in 2009 orbiting a tiny, dim star. Yet 55 Cancri e's orbit is more like that of the denser, inferno worlds CoRoT-7b and Kepler-10b. "What makes 55 Cancri e so remarkable is that despite its high temperature, the planet has a low density," said Demory.

Previously, a separate international team of astronomers had made observations of 55 Cancri e in visible light with Canada's MOST telescope. Initially, their evidence implied that 55 Cancri e's diameter was smaller by 25 percent, leading to reports of 55 Cancri e as actually the densest planet known. Refinements to those observations, however, now agree with the new Spitzer findings, which rely on a transit seen in longer-wavelength infrared light.

Exoplanetary Origins and Future Demise

No longer looking like a dense planet of solid rock, 55 Cancri e instead appears to be an unprecedented world with an intriguing history. The Spitzer results suggest that about a fifth of the planet's mass must be made of light elements and compounds, including water. In the intense heat of 55 Cancri e's terribly close sun, those light materials would exist in a "supercritical" state, between that of a liquid and a gas, and might sizzle out of the planet's surface.

New developments in planetary formation and evolution theory will probably be necessary to explain 55 Cancri e's back story. According to our models of the birth of solar systems, for example, 55 Cancri e could not have formed so near its star. Maybe it started out as a more distant planet with a large gaseous atmosphere. As worlds took shape in the 55 Cancri solar system, gravitational interactions amongst the system's five known planets could have prodded a young 55 Cancri e to migrate in toward its sun. In the process, the Neptune-like exoplanet might have lost most of its atmosphere, exposing a core that sputters with the venting of heated chemicals.

It seems certain that 55 Cancri e is on a "death spiral," soon to be devoured or ripped apart by its host star. But for now, the world's serendipitous placement in our sky will allow Spitzer and other instruments to study 55 Cancri e in further detail, expanding our knowledge of how exoplanets work.

"55 Cancri e orbits a very bright star thus enabling the possibility of obtaining a wealth of observations with space-based facilities at various wavelengths," said study co-author Michael Gillon of the University of Liege in Belgium and principal investigator for the warm Spitzer program aimed at detecting transiting low-mass exoplanets. "This fact will make 55 Cancri e a landmark for our understanding of the planetary interior and atmospheric composition of super-Earths."

Other authors of the paper are Diana Valencia, Sara Seager and Bjorn Benneke of MIT; Drake Deming of the University of Maryland; Christophe Lovis, Michel Mayor, Francesco Pepe, Didier Queloz, Damien Ségransan, and Stéphane Udry of the University of Geneva; and Patricio Cubillos, Joseph Harrington, and Kevin B. Stevenson of the University of Central Florida.

Source: Spitzer Space Telescope

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