Discovery of a New Planet
The excitement was palpable when researchers discovered a planet orbiting the star 40 Eridani A. However, it turns out that ‘Vulcan’ does not exist after all.
A Brief History
Do you remember when, in 2018, scientists announced the discovery of a planet that supposedly orbited the star 40 Eridani A? Star Trek fans were thrilled because this star was home to the fictional planet Vulcan, the birthplace of the character Mr. Spock in the famous Star Trek series. Last year, this discovery was already questioned, and now it is definitively clear: ‘Vulcan’ only exists in the realm of fiction.
A Super-Earth
Six years ago, astronomers used the Dharma Endowment Foundation Telescope to study the star 40 Eridani A. This led to the discovery of ‘Vulcan’ (officially designated as HD 26965 b or 40 Eridani b). The planet was thought to be a super-Earth located just 16 light-years from Earth. Researchers estimated that the planet was about twice the size of Earth (or slightly smaller than Neptune), orbiting its star every 42 days. Additionally, it was believed to be within the habitable zone!
Reevaluation of the Findings
The news that Vulcan does not actually exist is not a complete surprise to the original discoverers. In their research, they had already warned that the evidence for the presence of Vulcan might not indicate a real planet but rather disturbances within the star itself. Recent analyses, utilizing highly accurate radial velocity measurements not available in 2018, have now confirmed that the cautious stance on the possible discovery was indeed justified.
Small Oscillations
What exactly happened? When scientists ‘discovered’ the planet in 2018, they did not observe it directly. Instead, they inferred its existence from small oscillations in the motion of the parent star.
In short, the existence of 40 Eridani b was determined by observing changes in the star’s spectrum, suggesting it was moving back and forth. But last year, researchers brought disappointing news: their study concluded that these spectral changes were not caused by a planet tugging on the star but by activity on the star’s surface.
NEID Instrument
A new study further supports these findings. A recent research team studied 40 Eridani A using an instrument called NEID, which was recently added to the telescope complex at Kitt Peak National Observatory in Arizona. NEID, like other radial velocity instruments, uses the Doppler effect: changes in a star’s light spectrum that indicate its wobbling movements.
In this case, analyses of the supposed planet signal at different wavelengths from various layers of the star’s outer shell (photosphere) showed significant differences between individual wavelength measurements (Doppler shifts) and the total combined signal. This likely indicates that the planet signal was actually caused by stellar surface activity coinciding with a rotation period of 42 days. Think of convective swirling of hotter and cooler layers beneath the star’s surface, combined with stellar surface features such as spots and bright, active regions. Both can alter the radial velocity signal of a star.
Lessons for Future Exoplanet Searches
Although the hope of finding the planet Vulcan around the star 40 Eridani A has faded, the news is not entirely negative. The study provides an important lesson for future exoplanet searches. The demonstration of fine-tuned radial velocity measurements suggests that we will be better equipped to distinguish actual planets from surface movements on distant stars. This means that finding planets that truly exist has become slightly easier.
