A research team led by Paul Robertson, an assistant professor of astronomy at UC Irvine, has confirmed a new super-Earth orbiting in its host star's habitable zone roughly 25 light-years from our solar system — close enough, in astronomical terms, to be considered a genuine neighbor. The discovery, published in The Astrophysical Journal, adds GJ 3378b to a short list of nearby planets where the basic conditions for liquid water plausibly exist.
A Planet Built From Wobbles in Starlight
The team detected the planet using two instruments built specifically to find exactly this kind of world: the Habitable-zone Planet Finder on the Hobby-Eberly Telescope at McDonald Observatory in Texas, and the NEID Spectrometer on the WIYN Telescope at Kitt Peak National Observatory in Arizona. Both instruments work by measuring the tiny gravitational wobble a planet induces in its host star's light — a technique that yields a minimum mass rather than a precise one. For GJ 3378b, that minimum comes out to just over twice Earth's mass, placing it squarely in the "super-Earth" category that has become one of the most common — and most interesting — planet types astronomers now regularly find.
Co-authors on the discovery include Michael Endl and William Cochran of the University of Texas at Austin and McDonald Observatory, Gudmundur Stefansson of Schmidt Sciences, and Suvrath Mahadevan of Pennsylvania State University.
Right at the Edge, Not Comfortably Inside
What makes GJ 3378b worth attention isn't just its size or proximity — it's where it sits relative to its star. The planet receives approximately 90% of the stellar radiation Earth receives from the Sun, putting it inside the conventional habitable zone, the range of orbital distances where a rocky planet could plausibly maintain liquid surface water. But the research team is careful to flag that GJ 3378b sits near what astronomers call the "cosmic shoreline" — a rough boundary, observed across the planets and moons of our own solar system, past which stellar radiation becomes intense enough to strip a planet's atmosphere away entirely over geological time.
That distinction matters enormously, because habitable-zone placement alone guarantees nothing. Venus and Mars both orbit within reasonable distance of conditions that could support liquid water, and neither has retained an atmosphere capable of doing so. Whether GJ 3378b still holds onto its atmosphere — or ever had one — is, at this stage, a genuinely open question the discovery paper doesn't and can't answer.
The Wait for an Answer
Resolving that question will require more than the radial-velocity technique used to find the planet in the first place; it needs a telescope capable of directly imaging GJ 3378b and analyzing light that has passed through (or been blocked by) any atmosphere it might have. That capability doesn't exist yet. NASA's Habitable Worlds Observatory, designed specifically for this kind of direct exoplanet imaging, isn't expected to launch until the 2040s. If it eventually confirms an atmosphere around GJ 3378b, the next step — a search for biosignature gases, the same kind of chemical fingerprinting at the center of the ongoing K2-18b debate — would follow. For now, GJ 3378b joins the growing catalog of worlds that are close enough, and positioned well enough, to be worth the two-decade wait to find out.