JWST hunts for an 'Earth-moon' twin in a habitable zone, but the star has other plans

April 27, 2026 JWST hunts for an 'Earth-moon' twin in a habitable zone, but the star has other plans by Andy Tomaswick, Universe Today edited by Lisa Lock, reviewed by Andrew Zinin Lisa Lock scientific editor Meet our editorial team Behind our editorial process Andrew Zinin lead editor Meet our editorial team Behind our editorial process Editors' notes This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: fact-checked preprint trusted source proofread The GIST Add as preferred source Image of the TOI-700 system, including graphs of their habitable zones. Credit: NASA/JPL-Caltech/Robert Hurt/NASA’s Goddard Space Flight Center The moon has played a huge role in the development of Earth. It stabilizes the planet, tempers dramatic climate swings, and possibly even provides the tidal heating that might have led to the first life forms. So it's natural we would want to find a similar Earth/Luna system somewhere else in the cosmos. But astronomers have been searching for one for years at this point to no avail. And a new paper, available on the arXiv preprint server, from Emily Pass and her colleagues at MIT, Harvard, and the University of Chicago describes using the James Webb Space Telescope to track some of the most promising exomoon candidates—only to be foiled by the star they were orbiting. That star is TOI-700. Located about 100 light years away from Earth, TOI-700 is a small M-dwarf star that has a wide variety of known exoplanets, including two Earth-sized ones in the "habitable" zone, known as TOI-700 d and TOI-700 e. According to the paper, these planets are the best candidates we have for holding onto a stable moon, due to their proximity and gravitational pull. Turning the world's most powerful space telescope towards them offered our best chance to catch one in action. It was certainly more than capable of improving our knowledge of the planets themselves. Data described in the paper increased the accuracy of our orbital estimates of the planets by an order of magnitude, and improved our measure of their radius (1.145 times Earth for d and 0.919 times Earth for e) by a factor of 2 to 3. But one thing it couldn't do was find definitive evidence of a moon orbiting either planet. In theory, the telescope itself is more than capable of it. The researchers calculated that, in order to detect a Luna-analog, JWST would need to detect a 20 parts per million (ppm) dip in starlight. It is perfectly capable of doing so, but in fact, it might just be too good. Fraser talks Exomoon Hunting with Dr. Alex Teachey. Credit: Universe Today When analyzing the data, the research team realized there was a repeating noise pattern known as "red noise." This signal is caused by stellar granulation—the boiling and bubbling that happens in the plasma on the surface of a star. The signal itself oscillated every 16 minutes and had an amplitude of around 46 ppm—essentially washing out any 20 ppm signal a moon might give off. The best conclusion the researchers could draw with that level of certainty was that their observations were only sensitive to moons larger than Ganymede (the largest moon in our own solar system) on orbits longer than 2 days. That's not much of a constraint, but there was a bit of a silver lining. The researchers also determined that, if someone was able to develop a noise-reducing algorithm that can remove the…

This excerpt is published under fair use for community discussion. Read the full article at Phys.org.