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Alien Discovery by Citizen Scientists: Two Gaseous Planets Orbiting a Bright Sun-Like Star

At night, seven-year-old Miguel likes to talk to his father Cesar Rubio about planets and stars. “I try to nurture that,” says Rubio, a machinist in Pomona, California, who makes parts for mining and power-generation equipmen

Now the boy can claim that his father also helped discover planets. Cesar Rubio is one of thousands of volunteers participating in Planet Hunters TESS, a NASA-funded citizen science project that searches for evidence of planets beyond our solar system, or exoplanets. Citizen science is a way for citizens to collaborate with scientists. More than 29,000 people worldwide have joined the Planet Hunters TESS effort to help scientists find exoplanets.

Planet Hunters TESS has now announced the discovery of two exoplanets in a study published online in Monthly Notices of the Royal Astronomical Society, co-authoring Rubio and more than a dozen other citizen scientists.

These exotic worlds orbit a star called HD 152843, which is located about 352 light-years away. This star is about the same mass as the Sun, but almost 1.5 times larger and slightly brighter. Planet b, about the size of Neptune, is about 3.4 times larger than Earth and completes an orbit around its star in about 12 days. Planet c, the outermost planet, is about 5.8 times larger than Earth, making it a “sub-Saturn”, and its orbital period is somewhere between 19 and 35 days. In our own solar system, both planets would be well within Mercury’s orbit, which is about 88 days.

Studying them together, both at the same time, is really interesting to narrow down theories about how planets form and evolve over time,” said Nora Eisner, a doctoral student in astrophysics at the University of Oxford in the United Kingdom and lead author of the study. .

TESS stands for Transiting Exoplanet Survey Satellite, a NASA spacecraft launched in April 2018. The TESS team used data from the observatory to identify more than 100 exoplanets and more than 2,600 candidates awaiting confirmation.

Even in an age of advanced computing techniques like machine learning, having a large group of volunteers look through telescope data is a great help to researchers. Since researchers can’t perfectly train computers to identify the signatures of potential planets, the human eye is still valuable. “That’s why many candidates for exoplanets are missed and why citizen science is great,” Eisner said.

In the case of HD 152843, citizen scientists looked at a plot that showed its brightness over a month of TESS observations. The light curve showed three distinct dips, meaning at least one planet could orbit the star. All 15 citizen scientists who looked at this light curve highlighted at least two transits, and some highlighted the light curve on the Planet Hunters TESS online discussion forum.

In the case of HD 152843, citizen scientists looked at a plot that showed its brightness over a month of TESS observations. The light curve showed three distinct dips, meaning at least one planet could orbit the star. All 15 citizen scientists who looked at this light curve highlighted at least two transits, and some highlighted the light curve on the Planet Hunters TESS online discussion forum.

To make sure the transit signals came from planets and not from another source, such as eclipsing stars, passing asteroids or the motions of TESS itself, scientists had to look at the star using a different method. They used an instrument called HARPS-N (the High Accuracy Radial velocity Planet Searcher for the Northern Hemisphere) at the Telescopio Nazionale Galileo in La Palma, Spain, as well as EXPRES (the Extreme Precision Spectrometer), an instrument at Lowell Observatory in Flagstaff, Arizona. . Both HARPS and EXPRESS look for the presence of planets by examining whether the starlight “waves” as a result of planets orbiting their star. This technique, called the radial velocity method, also allows scientists to estimate the mass of a distant planet.

While scientists couldn’t get a signal clear enough to locate the planets’ masses, they got enough radial velocity data to make mass estimates — about 12 times the Earth’s mass for planet b and about 28 times the Earth’s mass for planet c. Their measurements confirm those signals that indicate the presence of planets; more data is needed for the confirmation of their masses. Scientists continue to observe the planetary system with HARPS-N and hope to have more information about the planets soon.

Researchers may soon have high-tech tools to see if these planets have atmospheres and what gases are present in them. NASA’s James Webb Space Telescope, due to launch later this year, will be able to look at the types of molecules that make up the atmospheres of planets like those in this system, especially the larger outer planet. The planets HD 152843 are far too hot and gaseous to support life as we know it, but they are valuable to study as scientists learn about the range of possible planets in our galaxy.

We are taking small steps toward finding an Earth-like planet and studying its atmosphere, and continue to push the boundaries of what we can see,” Eisner said. The citizen scientists who classified the HD 152843 light curve as a possible source of transiting planets, in addition to three moderators from the Planet Hunters discussion forum, were invited to have their names listed as co-authors of the study announcing the discovery of these planets.

One of these citizen scientists is Alexander Hubert, a student focusing on mathematics and Latin in Würzburg, Germany, with plans to become a high school teacher. So far, he has classified over 10,000 light curves through Planet Hunters TESS. “I sometimes regret that in our time we have to limit ourselves to one, maybe two subjects, as for me, Latin and Mathematics,” Hubert said. “I’m very grateful to have the opportunity to participate in something different on Zooniverse.”

Elisabeth Baeten of Leuven, Belgium, another co-author, works in reinsurance administration and says classifying light curves on Planet Hunters TESS is “relaxing”. Interested in astronomy since childhood, she was one of the original volunteers of Galaxy Zoo, an astronomical citizen science project launched in 2007. Galaxy Zoo invited participants to classify the shapes of distant galaxies.

While Baeten was part of more than a dozen studies published through Zooniverse projects, the new study is Rubio’s first scientific publication. Astronomy has been a lifelong interest, and something he can now share with his son. The two sometimes watch the Planet Hunters TESS website together.

I feel like I’m contributing, even if it’s just a small part,” Rubio said. “Scientific research in particular, it gives me satisfaction.” NASA has a wide variety of citizen science collaborations on topics ranging from Earth sciences to the sun to the greater universe. Anyone in the world can participate. View the latest options on