The James Webb Space Telescope (JWST) has opened up many wonders of the cosmos to scientists since it began its science operations a few years ago. But one thing that it hasn’t done is find an “exomoon”. These, as yet still theoretical, moons orbit exoplanets in other star systems, and JWST was supposed to find a plethora of them. However, so far it has found precisely none. It seems the cause is noise in the telescope’s instrumentation or noise from the star itself. But a new paper, available in pre-print form on arXiv from David Kipping, an astronomer at Columbia and also the host of the Cool Worlds YouTube Channel, shows how JWST can, in fact, find an exomoon. It likely just has to look for one in the same place repeatedly.
To prove the point, Dr. Kipping analyzed a bunch of data JWST collected on a planet called LP 890-9 c. This exoplanet orbits an ultra-cool red dwarf located around 105 light years away. With an 8.46-day orbital period, saying the planet is close to its star is an understatement, but, at least in theory, it is in the habitable zone of this extremely low temperature host star. One other advantage it had was how often and how long JWST took a look at it – Dr. Kipping was able to analyze data from twelve different transits.
Previous efforts to detect exomoons relied simply on a single transit. For example, JWST watched the gas giant Kepler-167 e, hoping to spot a small moon in orbit around it. But “red noise” confused the computer models analyzing the data, making it impossible to detect any moon that was much smaller than the Earth itself. “Red noise” is caused by slow, wandering changes in the detector, such as when it’s warming up, its “pointing” drifts slightly, or even by solar spots on the surface of the star itself.
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Fraser interviews Dr. Kipping – the author of the paper – about exomoons.
The key, according to Dr. Kipping, is averages. Exomoons have to obey the laws of physics, so they have to be at a certain place at a certain time around the planet. They don’t simply pop up where an instrumental glitch happened. And, crucially, instrumental glitches (and sun spots) don’t happen the same way every time for multiple transits. Over time, those glitches and spots can be smoothed out, leaving a clean view of the starlight. In fact, even one of the twelve transits taken of LP 890-9 c suffered from noticeable “red noise”. But when its data was combined from just one other “clean” transit, the sensitivity to detecting an exomoon rose significantly.
Unfortunately, in this particular case, that still led to a null result – the authors were able to confirm, with 95% confidence, that there are no moons larger than 0.1 Earth radii surrounding LP 890-9 c. That means no Ios, or Europas, or even Enceladuses. But it is by far the most sensitive moon hunt ever conducted outside our solar system.
Funnily enough, Dr. Kipping didn’t actually expect to succeed. LP 890-9 c orbits 0.04 AU from its star – less than a tenth of the distance between the Sun and Mercury. That means the gravitational tides from the star are absolutely brutal. Over the course of billions of years, those tidal forces will either strip a moon away, sending it out into deep space, or pull it inward, causing it to turn into rings. Simply put, a moon around LP 890-9 c would not survive for long.
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Fraser discusses the “secret weapon” for finding an exomoon.
So why did Dr. Kipping use that specific planet as an example? Because the paper is meant to define a proof of concept more so than act as an attempt to actually find the first exomoon. It proved that JWST doesn’t have a “noise floor” that prevents it from detecting relatively small moons, as so many astronomers had assumed in the past few years. It’s very capable of finding moons the size of our – provided astronomers decide to observe multiple transits.
Unfortunately that is easier said than done. Time on JWST is one of the most precious commodities in astronomy. It is responsible for everything from peering back to the first epochs of the universe to trying to track moons much closer to home. But, if we hope to find an exomoon for the first time using this set up equipment, it appears to be feasible. We just need more time.
Learn More:
D. Kipping – JWST Excludes Exomoons Down to 0.1 Earth Radii Around a Rocky, Temperate Exoplanet
UT – Finding Exomoons Using Their Host Planet’s Wobble
UT – JWST Hunts for an ‘Earth-Moon’ Twin in a Habitable Zone, But the Star Has Other Plans
UT – The Ambitious Plan to Spot Habitable Moons Around Giant Planets
About the Author
Source: Universe Today
