NASA’s Transiting Exoplanet Search Satellite (TESS) may have discovered its first free-floating or “orphan” planet. This is a planet wandering alone in the universe, without a star.
The potential discovery suggests that TESS could use it to detect these so-called rogue planets, a phenomenon first proposed by Albert Einstein 100 years ago.
Having discovered more than 5,000 exoplanets that exist in such an arrangement, it is estimated that the Milky Way is populated with numerous free-floating rogue planets, although we are most familiar with planets orbiting a host star (or stars). , more.
In fact, our galaxy may contain as many as a quadrillion (10 followed by 14 zeros) rogue planets that have been ejected from their host systems by gravitational interactions with other planets or stars. This means that the number of free-floating worlds may far exceed the number of stars in the Milky Way. Therefore, it is of great importance that TESS, launched in 2018, detects such a cosmic orphan.
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“We discovered the first signal in the TESS data that is consistent with what would be expected from microlensing a free-floating planet,” said Michelle Kunimoto, co-leader of the team, a postdoctoral researcher specializing in exoplanet detection at the Massachusetts Institute of Technology (MIT). she told Space.com.
“This was the first sector we investigated among the 75 sectors observed by TESS, and each sector corresponded to approximately 27 days of TESS observations,” Kunimoto continued. “It was surprising but really exciting to find something so early.”
The team tells Space.com that if this signal indeed points to a rogue exoplanet, it would likely be a planet several times the mass of Earth and 6,500 light-years away.
A little “bandit hunting” help from Einstein
The majority of exoplanets detected so far have been given clues thanks to their impact on their parent stars. This could be a “wobble” in the star’s motion caused by the small gravitational pull of an orbiting planet, or a dip in light that occurs as an orbiting planet passes or “transits” across the face of its star.
But without a parent star, none of these methods are valid. This is what makes rogue planets so difficult to detect.
“Rogue planets, as you might expect, are dark and don’t orbit any stars, which means the usual techniques for detecting exoplanets don’t really work,” Kunimoto said.
Fortunately, Einstein’s 1915 theory of gravity, better known as general relativity, predicts a phenomenon that can be used to detect these free-floating exoplanets.
Einstein proposes that massive objects warp the fabric of space and time, or space-time, and that gravity results from this curvature. When light passes through one of these curved points in space-time, its path becomes bent. This means that light from a background source, such as a star or galaxy, may take different paths around the intervening “lensing” object and therefore reach the observer’s view at different times.
This phenomenon is called “gravitational lensing” and causes the position of the background source to change from the observer’s perspective or to appear in more than one place in the same image.
Since rogue planets have very little mass, the lensing effect is weak and is therefore called “micro lensing”. However, this could cause a background source visible to astronomers to shine, indicating the presence of a rogue planet.
“Microlensing is the best and often only option for finding these dark, isolated objects because it relies solely on a planet’s mass through its gravitational field,” Kunimoto said. said.
Forget the “T” in TESS
As the “T” for transit in TESS suggests, this space telescope may not immediately seem like the right tool to hunt for rogue planets.
“TESS is designed to look for planets closely bound to their host stars by searching for transits,” Kunimoto explained. “Transits are ‘dimming’ of the star caused by a planet passing in front of it, as you may have seen in the last eclipse.”
However, as mentioned above, gravitational lensing can also cause the background star to brighten as a lensed object passes between that star and Earth. Kunimoto explained that because TESS is sensitive to small changes in a star’s light, it can also detect these flare episodes, a hallmark of microlensing caused by free-floating planetary rogues.
But given all this, you may wonder: Why is this the first potential rogue exoplanet among the 6,000 or so other exoplanet candidates (400 or so confirmed) that TESS has detected since 2018?
It turns out no one was really looking until now.
“TESS is surprisingly well-suited to finding rogue planets through microlensing, but it turns out that these types of signals haven’t really been investigated in TESS data before,” Kunimoto said. “Our approach to searching for individual planets with microlensing and the resulting TESS planetary microlensing candidate were firsts for TESS.
“Because TESS data has not been used to look for short-period microlensing events before, past exoplanet searches would not have been sensitive to seeing these signals.”
Unfortunately, like many other identified exoplanet candidates, this discovery still needs to be confirmed.
“It’s important to say that we cannot confirm that this is a planet at this time,” Kunimoto said. “The lack of recurrence of microlensing events means that it is difficult to discern the nature of any signal. We are therefore cautious about the origin of this event and call it a stray planet ‘candidate’ because it is consistent with the signal you are receiving.” “It is expected from such a world.”
He added that as the team explores more TESS data and makes follow-up observations, the truth about the signal will gradually become clear.
However, the tentative nature of these findings certainly did not dampen the team’s enthusiasm or excitement.
“Absolutely ten out of ten excitement from me,” team co-leader William DeRocco, a researcher at the University of California Santa Cruz, told Space.com. “I’m used to looking for dark matter because the odds of us seeing anything are extremely low, so the potential to discover something like a rogue world drifting in the darkness of interstellar space is incredible.”
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The authors of this study believe that the future is bright when it comes to the possibility of TESS discovering more rogue planets.
“This is a proof of principle that TESS can find such signals, and now it’s up to us to start diving deeper to find more and understand what they mean,” Kunimoto said. With 99% of the TESS data left, we have lots of new opportunities for exciting discoveries along the way!
The team’s research has been submitted for publication in the journal Monthly Notices of the Royal Astronomical Society. It is currently included in the arXiv repository as a pre-peer review article.