Relative size of TRAPPIST-1 to the sun.

Photo courtesy of NASA / ESO

Relative size of TRAPPIST-1 to the sun.

March 6, 2017

Cornell Astronomical Society Members Analyze NASA’s Exoplanet Discovery

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If planet hopping is your notion of a relaxing vacation, then a recent NASA discovery may be for you.

On Feb. 22, NASA announced that it had found seven earth-size planets orbiting a single star in the constellation Aquarius. Scientists named this exoplanet system TRAPPIST-1, for the Transiting Planets and Planetesimals Small Telescope they used to make the discovery.

Located at a miserly distance of 40 light years from Earth, TRAPPIST-1 includes three planets located in the ‘goldilocks’ zone, within the distance range for liquid water to exist. Consequently, NASA scientists believe these three to be the most hospitable within the system.

The Sun spoke with members of Cornell’s Astronomical Society and the astronomy department to understand the importance of the discovery.

“It’s very difficult to have that much mass around such a tiny star,” said CAS President Zach Murray ’18.

According to Murray, the most exciting aspect of the discovery was not the possibility of finding extraterrestrial life. Instead, it challenges existing ideas about the efficiency of planet formation and may mean that scientists have been underestimating the limits of planetary systems.

“Previously we were finding systems which were different from one another. Now we’re getting to the point of finding systems like ours,” said CAS Vice President William Woodruff ’18.

“If anything, this confirms the astronomy communities’ focus to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. The six inner planets around TRAPPIST-1 have orbital periods that are near-integer ratios. This strongly suggests that the planets formed further from their stars and then migrated inwards.” said Prof. Alexander Hayes, astronomy.

Scientists find exoplanets by tracking the brightness of stars. Momentary dimming indicates that a planet may have passed in front of it. According to Woodruff, scientists confirm the existence of an exoplanet when this dimming occurs at least three times.

Using this technique, however, poses significant challenges. Waiting for three orbits usually takes years and detecting miniscule changes in brightness from objects light years away requires extremely precise instruments.

“It’s like detecting a firefly passing in front of a lighthouse 50 miles away,” Woodruff explained.

Along with further study on how these planets formed, scientists will examine their atmospheric content. According to Murray, a particularly important reason for doing so is that certain gases do not coexist for long periods of time without something producing them.

“If you see a planet with both oxygen and methane in its atmosphere it’s a probable indicator of life,” Murray said.

Scientists analyze the chemical composition of a planet’s atmosphere using a technique known as spectroscopy. Using the fact that different gases reflect different wavelengths of light, scientists measure the intensities of these wavelengths from a particular planet and infer its composition.

According to Woodruff, such analysis is often reserved for larger planets because it is usually very difficult to use the technique on smaller ones, such as the ones in the TRAPPIST system.

Hayes, however, asserts that there are aspects of this system that make such analysis easier.

“Typically, Earth-sized bodies are difficult to study because they are very small compared to the size of their star, making it difficult to isolate the light passing through the planet’s atmosphere from the stronger signal coming from the star directly. The planets in the TRAPPIST system, however, are orbiting very close to an ultra cool dwarf star, TRAPPIST-1, similar in size of Jupiter. Its smaller size optimizes the signal coming from the planet’s atmosphere and actually makes TRAPPIST a good candidate for in-depth studies of atmospheric properties,” Hayes said.

  • So it was “a recent NASA discovery”, eh? How about checking the authors list of the actual paper, – the lead authors are all from European institutions. Which also operate the telescope TRAPPIST which – what a surprise – discovered the TRAPPIST-1 system in the first place. NASA – through its Spitzer space observatory – later helped refine the understanding of this complex planetary system, but the discovery was 100% non-NASA, and the follow-up work led by non-NASA scientists. Fascinating lesson: there is intelligent life on our own planet … in other countries than the U.S.