A planet beyond the solar system that has been compared to Spock's homeworld Vulcan in the Star Trek franchise may have been nothing more than an illusion caused by a jittery star.
The extrasolar planet or "exoplanet" (a term for a planet outside of our solar system) was proposed to orbit a star called 40 Eridani A or "Keid," which is part of a triple star system located around 16.3 light-years from Earth. In Star Trek, this star is also home to the planet Vulcan. First announced in 2018, the planet caused quite a stir thanks to its similarities with Spock's fictional home planet.
A team of scientists led by astronomer Abigail Burrows of Dartmouth College now thinks that the "wobble" of this planet's parent star isn't the result of an orbiting world tugging on it at all. Burrows and colleagues discovered using a NASA instrument called NEID located at Kitt Peak National Observatory that the origin of this wobble is actually "pulses and jitters" of Keid itself.
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The fictional version of Vulcan was first introduced during Gene Roddenberry's seminal original series run of Star Trek, mentioned in the 1965 unaired pilot episode "The Cage." In the 2009 J.J. Abrams-directed Star Trek reboot, Vulcan was destroyed by a time-traveling enemy of Kirk, Spock, and the rest of the Enterprise crew.
By wiping out the real-life Vulcan, officially designated HD 26965 b, this new research shows that sometimes life imitates art.
Sorry Keid, you're on your own...
There are several ways to detect exoplanets orbiting distant stars, but the two most successful techniques are the transit method and the radial velocity method. Both of these techniques consider the effect an orbiting planet has on its star.
The transit method, employed to great success by NASA's Transiting Exoplanet Survey Satellite (TESS), measures the tiny dips in light a planet causes as it crosses the face of its parent star.
While the transit method is by far the more fruitful of these two exoplanet detection methods, the radial velocity method is useful for spotting exoplanets that don't pass between the face of their star and our vantage point in the solar system.
The radial velocity method uses tiny shifts in the light of a star as an orbiting planet gravitationally tugs on it. As a star is pulled away from Earth, the wavelength of the light it emits is stretched, causing it to move to the "red end" of the electromagnetic spectrum, a phenomenon called "redshift." The converse happens when the star is pulled toward Earth, the wavelengths of light compress, and the light is "blue-shifted" toward the "blue end" of the electromagnetic spectrum.
This is analogous to the Doppler effect, which impacts sound waves on Earth. When an ambulance races toward us, the soundwaves from its siren are compressed, making them sound higher-pitched. When the ambulance races away, the sound waves are more spaced out, and the siren becomes lower-pitched.
The radial velocity method is best for detecting especially massive planets, as these exert a larger gravitational pull on their stars and thus generate a more pronounced shift in the starlight from that stellar body. However, it is less robust for detecting planets with masses lower than that of Jupiter, the solar system's most massive planet.
When HD 26965 b was first potentially detected using the radial velocity method, its mass was estimated to be about 8 times greater than that of Earth but less than that of Neptune, making it a so-called "super-Earth" planet. The faux-Vulcan was suspected to orbit its parent star at around 22% of the distance between Earth and the sun, completing a year in around 42 Earth days.
Yet even the scientists who discovered this planet warned that it could be a misdetection caused by Keid's inherent jitteriness. By 2023, researchers had cast major doubts on the existence of this exoplanet. These new high-precision radial velocity measurements, which were not yet available in 2018, are the final nail in the coffin of the Vulcan-like HD 26965 b.
The disappointing news for Star Trek fans was delivered by NEID, the name of which rhymes with "fluid." NEID is an instrument that uses radial velocity to measure the motion of nearby stars with extreme precision.
NEID separated out the suspected planetary signal into its constituent wavelengths representing light emitted from various layers in the structure of Keid's surface or photosphere. This allowed the team to detect significant differences in the individual wavelengths compared to the total combined signal.
The upshot is that the signal implied the existence of HD 26965 b is actually the result of something flickering at the surface of Keid approximately every 42 Earth days. This effect could also be created when hot and cold plasma rises and falls through Keid's convection zone and interacts with surface features like dark sunspot patches or bright, active regions called "plages."
While this discovery isn't great news for Keid and its planetary prospects, or for fans of Star Trek, it is a positive step for exoplanet-hunting scientists.
That's because the finely tuned radial velocity measurements of NEID promise that planetary signals can be more accurately separated and distinguished from the natural jitters of stars in the future.
The team's research is published in The Astronomical Journal.
