Small Mission to Shed New Light on Exoplanet Atmospheres

Image credit: NASA’s Goddard Space Flight Center/Francis Reddy

A SmallSat mission called Pandora seeks new uses for well-known spectroscopy tools to doublecheck the compositions of exoplanet atmospheres that may have previously been misidentified due to fluctuations in the light of their host stars. “

Pandora would be about a meter high and about half a meter wide, and it has two primary ways of measuring,” said Thomas Barclay, a research scientist at the University of Maryland Baltimore County and Goddard. “Light received by the telescope goes behind the mirror and is split into a visible light channel, which will be primarily used for measuring the brightness of the star over time, and an infrared channel, which we primarily use for understanding exoplanet atmospheres.”

Most of the 4,400 planets found outside our solar system were discovered because they periodically block light from their host stars – an event called a transit –as seen from our perspective on Earth. In order to obtain accurate measurements of the star’s brightness before and during the planet’s transit, the analysis methods assume the star’s disk is uniformly bright. However, this is not the case.

One way starlight fluctuates is the presence of bright or dark spots rotating into and out of view. These features increase and decrease during the star’s activity cycle. Goddard research scientists Elisa Quintana and Barclay are working on a technology that takes that fluctuation into account.

Different chemicals absorb light at different colors, which is true for the gases in exoplanet atmospheres too. Using a spectrometer, astronomers can study which wavelengths are absorbed, which reveals the gases that make up a planet’s atmosphere.

“The beauty of Pandora is that none of the individual things we are trying to do are new, but packaging them together in a small spacecraft is innovative,” Barclay said. P

andora’s infrared sensor was designed originally for the James Webb Space Telescope, and the mirror technology has also been used in previous missions.

The mission would be the first satellite to undertake long-duration study of exoplanets using both visible infrared detectors at the same time, Quintana said. These instruments have never been included on an Astrophysics SmallSat before, which adds complications to the design.

The limited size associated with a SmallSat, analogous to a small washing machine, presented an important challenge for the Pandora team. The infrared camera in particular must operate at very low temperatures, requiring a cryocooler. This, along with the necessary electronics to allow the spectrometers to work, complicates the design, as specific components of the satellite must remain stable or cannot interact with sunlight.

The technology and research being completed in relation to Pandora can benefit future missions as well.

“Having simultaneous multi-wavelength observations is really how we are going to learn the most about complex phenomena like stellar activity and how it impacts planets,” Quintana explained, “so I think it’s something that people are going to want to duplicate.”

For research focused on finding Earth-sized planets around cool M dwarf stars, or studies on how the proximity of “active” stars, with numerous and powerful stellar flares, affects the habitability of nearby planets, satellites similar to Pandora will be extremely useful. Beyond that, Pandora can become a model for other low-budget, high-impact projects.

“As we have done with previous missions, future scientists can apply what we have learned about creating complex projects in a small volume and relatively constrained cost cap to their own missions.” Barclay said.

Pandora is a middle-sized mission under a new program called Pioneers, which has a $20 million cost cap. This opens the door to missions between Explorer size and research and development programs. Pandora fits within this range and was selected along with three other concepts to be studied for six months.

1. Pandora’s telescope has a 0.45 meter diameter aperture that will collect light for a visible channel, and will use a prism to split the light for an infrared channel. 2. Pandora will use transmission spectroscopy, a proven technique to identify the makeup of a planet’s atmosphere as it transits its host star.

(Image credit: Lawrence Livermore National Lab and NASA’s Goddard Space Flight Center)

After a review process, Pandora may be selected to continue through the Pioneer program. If so, construction of the spacecraft and telescope can begin in partnership with the Lawrence Livermore National Lab.

The Pioneer program allows missions like Pandora, which provide opportunities for scientists to explore ideas that can be accomplished through lowerbudget missions. “SmallSats enable early career scientists, and that enables us to have a diverse team,” Quintana said.

Quintana focused on allowing a diverse group of early career scientists to lead the mission’s science, engineering and management. By opening the doors for newer scientists to gain experience in leadership and focus on a unique science case, she said, the next generation of spaceflight leaders matures. Barclay also noted the importance of this aspect of Pandora, highlighting how a high number of the leadership are women and Hispanic scientists.

“That makes Pandora stand out as doing things differently, and I think doing things better than we have done in the past,” Barclay said. The investments in the updated usage of spectroscopy technology as well as the future generations of diverse scientists create a noteworthy project out of Pandora.

“We are a small mission,” Barclay said, “but we can do groundbreaking science.”

CONTACTS

Elisa.Quintana@nasa.gov or 301-286-0851

Thomas.Barclay@nasa.gov or 301-286-5079