It would explain a lot if two recent discoveries involving 'mini-Neptunes' turned out to be representative of what happens to their entire class. For Michael Zhang (Caltech) and colleagues, in two just published papers, have found that mini-Neptunes can lose gas to their parent star, possibly indicating their transformation into a 'super-Earth.' If such changes are common, then we have a path to get from a dense but Neptune-like world to a super-Earth, a planet roughly 1.6 times the size of the Earth and part of a category of worlds we do not see represented in our Solar System. As we drill down toward finding smaller worlds, we've been finding a lot of mini-Neptunes as well as super-Earths, with the former two to four times the size of the Earth. Thus we have a bimodal gap in exoplanet observation. Where are the worlds between 1.6 and 2-4 times the size of Earth? The new work examines two mini-Neptunes around the TESS object TOI 560, located about a hundred light-years from Earth,...

Given our recent discussion of exomoon candidate Kepler-1708 b-i, a possible moon 2.6 times the mass of Earth orbiting a gas giant, I want to be sure to work in Miki Nakajima’s work on how moons form. Nakajima (University of Rochester) is first author of the paper describing this work. It’s a significant contribution because it points to a way to refine the target list for exomoon searches, one that may help us better understand where to look as we begin to flesh out a catalog of these objects.. And flesh it out we will, as the precedent of the rapidly growing exoplanet count makes clear. What I want to do today is consider how we’ve thus far proceeded. You’ll recall that when David Kipping and team performed their deep analysis of the data leading to Kepler-1708 b-i, they chose gas giants on orbits with a period of 400 days or more, so-called ‘cool worlds’ more like Jupiter than the ‘hot Jupiters’ found so frequently in early exoplanet studies. The method produced a strong candidate...

Half a century ago, we were wondering if other stars had planets, and although we assumed so, there was always the possibility that planets were rare. Now we know that they’re all over the place. In fact, recent research out of Katholieke Universiteit Leuven in Belgium suggests that under certain circumstances, planets can form around stars that are going through their death throes, beginning the transition from red giant to white dwarf. The new work homes in on certain binary stars, and therein hangs a tale. After a red giant star has gone through the stage of helium burning at its core, it is referred to as an asymptotic giant branch star (AGB), on a path that takes it through a period of expansion and cooling prior to its becoming a white dwarf. These expanding stars lose mass as the result of stellar wind, up to 50 to 70 percent of the total mass of the star. The result: An extended envelope of material collecting around the object that will become a planetary nebula, a glowing...

We started finding a lot of 'hot Jupiters' in the early days of planet hunting simply because, although their existence was not widely predicted, they were the most likely planetary types to trigger our radial velocity detection methods. These star-hugging worlds produced a Doppler signal that readily showed the effects of planet on star, while smaller worlds, and planets farther out in their orbits, remained undetected. David Kipping (Columbia University) uses hot Jupiters as an analogy when describing his own indefatigable work hunting exomoons. We already have one of these - Kepler-1625 b-i - but it remains problematic and unconfirmed. If this turned out to be the first in a string of exomoons, we might well expect all the early finds to be large moons simply because using transit methods, these would be the easiest to detect. Kepler-1625 b-i is problematic because the data could be showing the effects of other planets in its system. If real, it would be a moon far larger than any...

Using machine learning to provide an algorithmic approach to the abundant data generated by the Transiting Exoplanet Survey Satellite (TESS) has proven unusually productive. I'm looking at an odd object called TIC 400799224, as described in a new paper in The Astronomical Journal from Brian Powell (NASA GSFC) and team, a source that displays a sudden drop in brightness - 25% in a matter of four hours - followed by a series of brightness variations. What's going on here? We're looking at something that will have to be added to a small catalog of orbiting objects that emit dust; seven of these are presented in the paper, including this latest one. The first to turn up was KIC 12557548, whose discovery paper in 2012 argued that the object was a disintegrating planet emitting a dust cloud, a model that was improved in subsequent analyses. K2-22b, discovered in 2015, showed similar features, with varying transit depths and shapes, although no signs of gas absorption.. In fact, the objects...

As we begin the New Year, I want to be sure to catch up with the recent announcement of a discovery regarding 'rogue' planets, those interesting worlds that orbit no central star but wander through interstellar space alone (or, conceivably, with moons). Conceivably ejected from their host stars through gravitational interactions (more on this in a moment), such planets become interstellar targets in their own right, as given the numbers now being suggested, there may be rogue planets near the Solar System. Image: Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards...