Astronomy
Sorry Spock, But “Vulcan” Isn’t a Planet After All
In 2018, astronomers detected an exoplanet around the star 40 Eridani. It’s about 16 light-years away in the constellation Eridanus. The discovery generated a wave of interest for a couple of reasons. Not only is it the closest Super-Earth around a star similar to our Sun, but the star system is the fictional home of Star Trek’s Vulcan science officer, Mr. Spock.
It’s always fun when a real science discovery lines up with science fiction.
Eridani’s other name is HD 26965, and it’s actually a triple-star system. Astronomers discovered the system’s lone planet, Eridani b, using the radial velocity method. Orbiting planets tug on their stars, and the star’s movement creates a change in its spectrum. Astronomical telescopes with spectrometers can detect the changes.
Jian Ge, an astronomy professor at the University of Florida, led the study that presented the discovery in 2018. At the time, Ge said in a press release, “The new planet is a ‘super-Earth’ orbiting the star HD 26965, which is only 16 light years from Earth, making it the closest super-Earth orbiting another Sun-like star. The planet is roughly twice the size of Earth and orbits its star with a 42-day period just inside the star’s optimal habitable zone.”
A super-Earth in the habitable zone around a Sun-similar star ‘only’ 16 light-years away is an intriguing discovery. Its link with a beloved Star Trek character gave the discovery wings, and word spread.
However, in the intervening years, follow-up observations have not confirmed Eridani b’s existence. A 2021 study suggested that the change in the star’s spectrum was a false positive. Now, a new study says that the exoplanet fondly named Vulcan does not exist.
The study is “The Death of Vulcan: NEID Reveals That the Planet Candidate Orbiting HD 26965 Is Stellar Activity.” It’s published in The Astronomical Journal, and the lead author is Abigail Burrows, an astronomer at Dartmouth College.
“We revisit the long-studied radial velocity (RV) target HD 26965 using recent observations from the NASA-NSF “NEID” precision Doppler facility,” Burrows and her co-authors write. After a deeper, line-by-line analysis of the radial velocity data, “… we demonstrate that the claimed 45-day signal previously identified as a planet candidate is most likely an activity-induced signal.”
Activity-induced signal means that the signal comes from the star’s activity, not from the external tug of an exoplanet.
Vulcan’s initial detection was based on data from the Dharma Planet Survey (DPS.) DPS monitored about 150 nearby Sun-like stars for changes in their spectra. Data from the Keck Telescope and the HARPS planet-finding spectrograph also contributed to the discovery.
When the planet was detected in 2018, the discoverers recommended caution. They presented the data as they collected it, along with their best interpretation. That’s standard in science, and they were careful in calling it a candidate planet. In their paper, they also discussed “the possibility that the RV signal is actually produced by stellar rotation modulated activity.” That activity could be sunspots, convection irregularities, or other things.
But in the end, they concluded that what they were seeing was likely a planet.
“By carefully examining the RV data in the active and quiet phases of the star, and after carefully considering all possible stellar activity sources, we concluded that the coherent signal seen from HD 26965 is most likely from a planet, with some RV noise contributed by stellar activity,” the authors wrote in the 2018 paper.
The rest of us were happy to agree because finding a super-Earth around a nearby Sun-like star is the kind of thing we hope to find.
“Men sometimes see exactly what they wish to see.”
-Spock of Vulcan
Sadly for Vulcan, the newest research shows that the stellar activity isn’t noise. It accounts for the entire signal.
The new results are based on NEID, the NN-explore Exoplanet Investigations with Doppler spectroscopy. It’s a high-resolution spectrometer attached to the WIYN (Wisconsin-Indiana-Yale-NOIRLab) telescope at Kitt Peak Observatory. The researchers used NEID to capture 63 spectra from Eridani over a six-month period.
NEID revealed a lot of information about the star, including things like contrast and radial velocity. Together, NEID data paints a more complete picture of the star and its activity. In this new work, Burrows and her co-researchers showed that all of this activity lines up with the star’s 42-day rotation period.
“All measurements show a strong signal at or near the 42-day stellar rotation period,” they write.
This figure from the study shows NEID data on the left. “All data show clear rotational modulation at or near the 42-day period,” the authors write. The right shows periodograms for the data, which show “clear power at the stellar rotation period of ?42 days.” Image Credit: Burrows et al. 2024The authors write that their work “points toward a decaying starspot or plage” as the source of the signal. A plage is a bright spot on a star’s chromosphere. They used a variety of methods to reach this conclusion. “While each of these methods taken individually may not rule out a potential planetary signal at the same phase and period as the activity signal, collectively, our analyses show that an activity hypothesis is favoured over the specific planet claimed in Ma et al. (2018),” they conclude.
“When you eliminate the impossible, whatever remains, however improbable, must be the truth.”
Spock of VulcanThe authors of the new paper didn’t set out to debunk Vulcan. Their paper is part of an effort to better understand the periodic and quasi-periodic spectral changes from Sun-like stars. Without a better understanding, annoying false positives will cloud our understanding of exoplanets, especially Earth-like ones around Sun-like stars. “To reach the precision necessary to detect temperate, Earth-mass extrasolar planets (exoplanets) around Sun-like stars using the radial velocity (RV) technique, the community must improve Doppler measurement precision significantly from the current state of the art,” they write.
“Detecting and characterizing these exo-Earths is vital for future spaceborne direct imaging missions, which will set the scientific priorities for the coming decade,” the authors explain.
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NASA's Lucy Mission Reveals Asteroid's Strange Moon
The asteroid Dinkinesh surprised NASA’s Lucy mission when it turned out to have a moon. Now, scientists are taking a closer look at the pair’s formation.
The post NASA's Lucy Mission Reveals Asteroid's Strange Moon appeared first on Sky & Telescope.
Watch Chinese company launch 4 satellites to orbit from ship at sea (video)
A Mini-Neptune in the Habitable Zone in a Binary Star System
Sometimes, it seems like habitable worlds can pop up almost anywhere in the universe. A recent paper from a team of citizen scientists led by researchers at the Flatiron Institute might have found an excellent candidate to look for one – on a moon orbiting a mini-Neptune orbiting a star that is also orbited by another star.
That’s a lot of things orbiting each other, so let’s dive into some details of the star system known as TOI 4633. It has two potential planets. One has a relatively short 34-day orbit but whose existence was only found by radial velocity measurements, as it doesn’t cross between the Earth and its host star. It also has yet to be confirmed by exoplanet hunters.
Another planet, known for now at TOI 4633c, is much more intriguing. It falls into the size category of a “mini-Neptune,” meaning it is slightly smaller than the 8th planet in our solar system but is likely still a gas giant with a thick atmosphere. It orbits its host star once every 272 days – making it one of the 40 longest-orbiting planets out of the thousands discovered so far.
Binaries are just one of a class of multiple-star systems, as Fraser explains.That long orbit also puts it in the habitable zone of its host star – about .85 AU away from the G-type star it is orbiting. Being in the habitable zone would imply that liquid water could exist on its surface. However, the size of the planet and the likely density of its atmosphere would rule out the possibility of surface water on the planet itself.
However, there is a relatively good chance that TOI 4633c could have a moon. Planets with longer orbits tend to accrue them (hence why Venus and Mercury don’t have any in our own solar system). Such a small world wouldn’t have the same restrictive constraints as its gas-giant host planet, meaning it could potentially be habitable, such as the moons Pandora in the Avatar franchise or Endor in Star Wars.
But what makes this system even more unique is that the star TOI 4633c is orbiting is itself being orbited by another star. It wasn’t long ago that we weren’t even sure if planets could exist in these “binary” systems, and how strange life might be on one has become prominent recently with the popularity of The Three-Body Problem. But in theory, binary systems have habitable zones, and planets can survive in a stable orbit around at least one of the stars.
TESS’ primary mission is compete, but its data is still a treasure trove of new discoveries, as Fraser covers.The smaller star orbits around its larger binary companion only once every 230 years and gets close enough to the other star to be considered relatively close by interstellar standards. As of now, it’s unclear what, if any, effect this proximity to another star would have on TOI 4633c, but it’s doubtful that it would be a world like Tatooine.
However, the system lacks similarities to famous fictional examples, and it makes up for its potential to solve some long-standing problems in planetary formation theory. In addition to searching for a potential exomoon around TOI 4633c, scientists will continue to monitor the system closely to see if it remains stable. They can also see how the current known (and theorized) planets fit into existing models of planetary system formation.
This is another feather in the cap of the Planet Hunters TESS citizen science collaboration. There are undoubtedly more strange star systems out there for them to find. If you’re interested in helping them, you can sign up here.
Learn More:
NASA – Discovery Alert: Mini-Neptune in Double Star System is a Planetary Puzzle
Eisner et al. – Planet Hunters TESS. V. A Planetary System Around a Binary Star, Including a Mini-Neptune in the Habitable Zone
UT – Marvel at the Variety of Planets Found by TESS Already
UT – A New Venus-Sized World Found in the Habitable Zone of its Star
Lead Image:
Artist’s depiction of the binary system TOI 4633 and its potentially habitable planet.
Credit – Ed Bell for Simons Foundation
The post A Mini-Neptune in the Habitable Zone in a Binary Star System appeared first on Universe Today.
