Light From a ‘SuperEarth’ Detected for the First Time


The star 55 Cancri has been a source of joy and firsts for planet hunters. Not only was it one of the first known stars to host an extrasolar planet, but now the light from one of its five known planets has been detected directly with the Spitzer Space Telescope, the first time a ‘smaller’ exoplanet’s light has been detected directly. Planet “e” is a super-Earth, about twice as big and eight times as massive as Earth. Scientists say that 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. “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 first planet around 55 Cancri was reported in 1997 and 55 Cancri e – the innermost planet in the system — was discovered via radial velocity measurements in 2004. This planet has been studied as much as possible, and astronomers were able to determine its mass and radius.

But now, Spitzer has 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 (1,726 degrees Celsius, 3,140 degrees Fahrenheit), hot enough to melt metal.

In 2005, Spitzer became the first telescope to detect light from a planet beyond our solar system, when it saw the infrared light of a “hot Jupiter,” a gaseous planet much larger than 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.

The new information about 55 Cancri e, along with knowing it is about 8.57 Earth masses, the radius is 1.63 times that of Earth, and the density is 10.9 ± 3.1 g cm-3 (the average density of Earth is 5.515 g cm-3), places the planet firmly into the categories of a rocky super-Earth. But it could be 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, and the star can be seen with the naked eye. 55 Cancri e is 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.”

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.

Source: JPL

28 Replies to “Light From a ‘SuperEarth’ Detected for the First Time”

    1. @Scott – Nancy’s use of English looks all good and proper to me.

      Apostrophes are being used to denote possession or ownership here – I’m struggling to see what your problem is.

      1. Nope, he’s right. No apostrophe as it’s not possessive.

        But why on earth do we need to nitpick what’s really just a typo? You should read some of the “bigger” blogs out there if you want to appreciate how well Nancy is doing. 😉

      2. I was unable to image the apostrophe due to the glare of all the interesting words.

      3. the apostrophe denotes a missing “e” from the Old English Genitive ending “es” thus it would have been Super Earthes are more massive, a harder mistake to make, but who wants to write in Old English? I suspect Nancy is a victim of Ye Olde Cutte and Payste monster or the caption editor. Perhaps the prize for spotting such typos should be the chance to proof read Nancy’s next article after she has finished it and before the deadline of course 🙂

  1. I would HOPE our bodies emit more infrared than visible light. If you were emitting visible light that would likely mean you were on fire!

  2. The terminology can be really misleading at times (but maybe it’s just me)… my first thought was that this planet had been directly imaged, not that we had merely teased the planet’s light from the star’s light by seeing what happens when the planet disappears from view!

    Still a fantastic achievement though.

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  3. What about trying to block light of star while allowing light from star’s planets by very primitive means?
    Quick calculation – sphere with 1 m diameter and a telescope located some 100’000 km away would cover any dwarf star in our neighborhood while allowing light from any planet with fairly reasonable orbit (like 0.2 AU and more). Of course great stability and extremely precise navigation would be required, but I think it’s achievable with current technology. Maybe L4 and L5 points of Earth-Moon system would be suitable for placement? Or out-of-ecliptic orbit like Ulysses?

    1. That kind of instrument is known as a coronagraph (if attached to the telescope) or a starshade (if deployed as you describe). Coronagraphs have been used for the Sun for a long time and they are starting to come into use for exoplanet detection. The New Worlds Mission is a proposed starshade mission to be used in conjunction with existing and future telescopes.

      1. Thanks for the information! I’ve never heard about New Worlds before. If I uderstand that correctly, the starshade is very similar to coronograph – a tiny circle positioned very close to telescope (in order of metres). Dealing with diffraction is probably the biggest part of design.

      2. Well, the starshade is what you described – a separate spacecraft positioned thousands of kilometers away. This would allow it to be much bigger and take a more precise shape (I assume) that reduces the effects of diffraction.

        I hadn’t heard of it either until I researched for my earlier comment, and it sounds very exciting 😀 But I doubt it could be used en masse for imaging extrasolar planets… just getting it into position for one viable candidate star could takes weeks or months, given the distances involves (and therefore, fuel requirements) and need for precision.

      3. Fuel requirement is the reason why I tought about Earth-Moon lagrange points – the telescope would very slowly sweep whole plane of ecliptic as Earth orbits around the Sun and it’s possible to achieve relativly stable positions with low fuel requirements by using halo orbits.

      4. Nearly correct on cycle time. IIRC the missions plan to cycle through ~ 150 nearby stars within a mission lifetime. Say ~ 3 years, so ~ 50 stars a year, so ~ 1 week/star, so a few days observation time for each system.

  4. Paragraph 7 seems to suggest an atmosphere of sorts (vapour and steam) and paragraph 9 suggests no atmosphere of any significance. Looks to me like a little more work needed yet.

    1. Well, in the case of paragraph 9, “significance” means the atmosphere needs to be thick enough and have enough circulation to carry plenty of heat to the night side of the tidally-locked planet. It would still be a significant atmosphere by paragraph 7’s standards 🙂

  5. Naive question: how much more powerful would our telescopes have to be to actually see surface details of some of these planets at, say, 40 light years away?

    1. Depends on what you mean by surface details. The Spitzer telescope has already mapped exoplanet planet surfaces, due to well characterized telescope spreading functions and body rotation:

      “Spitzer measured the infrared light coming from the planet as it circled around its star, revealing its different faces. These infrared measurements, comprising about a quarter of a million data points, were then assembled into pole-to-pole strips, and, ultimately, used to map the temperature of the entire surface of the cloudy, giant planet.”

      1. I guess I mean something more detailed like the photos we get back from some of the probes in our own solar system taking shots of the planets and their moons.

      2. I on the other hand was trying to get a figure for the resolution you desired, as image processing is dependent on it more than direct photographic methods. (Whether or not you would call a modern telescope “photographic”, considering the integration times and active focusing that can be used.)

        There are estimates for that (depending on your desired resolution), meanwhile we can estimate the needed observatory to be sizable:

        “Planetary Assessment: The final step in extrasolar planet studies will be the ability to study these distant worlds in the same way that Earth-observing systems study the Earth’s surface. Such a telescope will of necessity be large, to collect enough light to resolve and analyze small details on the planet’s surface. However, these kinds of studies do not lie in the foreseeable future, for it takes square kilometers of collecting area to capture the needed signal.”

        I think they are then projecting resolutions of tens of meters, not the sub-meter one you are discussing. They want to see oceans and continents, and possibly redwood sized plants.

  6. When the adjectives run out:

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