Briefcase-sized satellite is smallest on record to spot a planet outside solar system

About twice the size of Earth, exoplanet 55 Cancri e is a 'scorching hot' planet and orbits extremely close to its Sun-like parent star


                            Briefcase-sized satellite is smallest on record to spot a planet outside solar system
ASTERIA (top center) (NASA/JPL-Caltech)

About the size of a briefcase, a spacecraft has broken the record for being the smallest satellite to detect an exoplanet — 55 Cancri e — that is, a planet outside our solar system. This proves that a tiny planet-hunting spacecraft can do complex tasks and pave the way for deploying similar ones in future missions.

Called Arcsecond Space Telescope Enabling Research In Astrophysics (ASTERIA), it belongs to a category of satellites referred to as CubeSats, which vary in size but are typically smaller than a suitcase. ASTERIA is a 6U CubeSat space telescope (roughly 10 cm x 20 cm x 30 cm, 10 kg), and was the first JPL-built CubeSat to have been successfully operated in space. It was launched to the International Space Station (ISS) with the SpaceX Falcon-9 Commercial Resupply Services 12 (CRS-12) mission on August 14, 2017. The spacecraft was deployed from the ISS on November 20, 2017. 

"Long before it was deployed into low-Earth orbit from the International Space Station in November 2017, the tiny ASTERIA spacecraft had a big goal: to prove that a satellite roughly the size of a briefcase could perform some of the complex tasks much larger space observatories use to study exoplanets. A new paper describes how ASTERIA didn't just demonstrate it could perform those tasks but went above and beyond, detecting the known exoplanet 55 Cancri e," says a statement from NASA's Jet Propulsion Laboratory (JPL). 

"This is the first detection of an exoplanet transit by a CubeSat. The successful detection of super-Earth 55 Cancri e demonstrates that small, inexpensive spacecraft can deliver high-precision photometric measurements," says the study, which has been accepted for publication in The Astronomical Journal. About twice the size of Earth, 55 Cancri e is described as a “scorching hot” planet and orbits extremely close to its Sun-like parent star. Scientists already knew the planet's location, and looking for it was a way to test ASTERIA's capabilities. The tiny spacecraft was not initially designed to perform science. Instead, the mission's goal was to test new technologies and develop new capabilities for future missions. The aim was to build a small spacecraft that could conduct fine pointing control — the ability to stay steadily focused on an object for long periods. 

The exoplanet 55 Cancri e is depicted with its star in this artist's concept (NASA/JPL-Caltech)

The CubeSat used fine pointing control to detect 55 Cancri e via the transit method, in which scientists look for dips in the brightness of a star caused by a passing planet. As 55 Cancri e blocks out only 0.04% of its host star's light, it was an especially challenging target for ASTERIA. The mission achieved "marginal detection", meaning the data from the transit, on its own, would not have convinced scientists that the planet existed. Scientists explain that faint signals that look similar to a planet transit can be caused by other phenomena. But the team confirmed that they were indeed seeing 55 Cancri e by comparing the CubeSat's data with previous observations of the planet. 

"This mission has mostly been about learning. We've discovered so many things that future small satellites will be able to do better because we demonstrated the technology and capabilities first. I think we've opened doors," says Akshata Krishnamurthy, co-investigator and science data analysis co-lead for ASTERIA at JPL, in the analysis. 

Based at JPL in Southern California and the Massachusetts Institute of Technology (MIT), the mission team engineered new instruments and hardware, pushing past existing technological barriers to create their payload. Though its prime mission was only 90 days, ASTERIA received three mission extensions before the team lost contact with it last December. "Detecting this exoplanet is exciting because it shows how these new technologies come together in a real application. The fact that ASTERIA lasted more than 20 months beyond its prime mission, giving us valuable extra time to do science, highlights the great engineering that was done at JPL and MIT," says Vanessa Bailey, the principal investigator for ASTERIA's exoplanet science team at JPL, in the report.

According to scientists, while it would not be possible to pack all the capabilities of a larger exoplanet-hunting spacecraft like NASA's Transiting Exoplanet Survey Satellite (TESS) into a CubeSat, they believe tiny spacecraft could play a supporting role for them. Small satellites, with fewer demands on their time, could be used to monitor a star for long periods in hopes of detecting an undiscovered planet. Scientists further say that after a large observatory discovers a planet transiting its star, a small satellite could also watch for subsequent transits, freeing up the larger telescope to do work smaller satellites cannot. 

Sara Seager, astrophysicist and principal investigator for ASTERIA at MIT, was recently awarded a NASA Astrophysics Science SmallSat Studies grant to develop a mission concept for a follow-on to ASTERIA. The proposal describes a constellation of six satellites about twice as big as ASTERIA that would search for exoplanets similar in size to Earth around nearby Sun-like stars.

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