---
title: UMD-Led Study Lifts Veil on Common but Mysterious Type of Exoplanet
date: 2025-05-06T05:30:00-04:00
author: University of Maryland
canonical_url: "https://today.umd.edu/umd-led-study-lifts-veil-on-common-but-mysterious-type-of-exoplanet"
section: Articles
---
# UMD-Led Study Lifts Veil on Common but Mysterious Type of Exoplanet

*May 6, 2025* — by [Maryland Today Staff](/author/maryland-today-staff)


> Webb Telescope Provides Rare Glimpse of Distant Planet Unobscured by Haze and Clouds

*TOI421b 1920x1080 — This artist’s concept shows what the hot sub-Neptune exoplanet TOI-421b could look like.*

Though they don’t orbit our sun, sub-Neptunes are the most common type of planet throughout the galaxy. Larger than Earth but smaller than Neptune, these gassy exoplanets are shrouded in mystery—and often, a lot of atmospheric haze—but a new University of Maryland-led study provides a new level of clarity.

The researchers theorized that TOI-421b, which orbits a star nearly 245 light years from Earth, would essentially have clear skies because of its relatively toasty temperatures—and they were right. Using NASA’s James Webb Space Telescope (JWST), they were able to get an unimpeded view, enabling them to detect water vapor and possibly carbon monoxide and sulfur dioxide in its atmosphere. They published the results Monday in *Astrophysical Journal Letters.*

“I had been waiting my entire career for Webb so that we could meaningfully characterize the atmospheres of these smaller planets,” said [Eliza Kempton](https://www.astro.umd.edu/people/ekempton.html), a UMD astronomy professor and principal investigator of the new study. “By studying their atmospheres, we’re getting a better understanding of how sub-Neptunes formed and evolved, and part of that is understanding why they don't exist in our solar system.”

Before JWST, most sub-Neptune atmospheres appeared to have flat or featureless transmission spectra, meaning that scientists couldn’t discern specific chemical fingerprints revealing the atmosphere’s composition. This led astronomers to conclude that certain sub-Neptunes were likely highly obscured by clouds or hazes.

In their latest study of TOI-421b, researchers used Webb to see features that were previously difficult to capture.


*chart that shows wavelength of light and amount of light blocked for exoplanet TOI-421b hot sub-Neptune — A transmission spectrum captured by NASA’s James Webb Space Telescope reveals the presence of water and the possible presence of sulfur dioxide and carbon monoxide, but no signs of carbon dioxide or methane, in the atmosphere of the hot sub-Neptune exoplanet TOI-421b. (Image courtesy of NASA, ESA, CSA, Joseph Olmsted \[STScI\])*




**Topics:** [Research](https://today.umd.edu/tags/research)


**Tags:** [Astronomy](https://today.umd.edu/topic/astronomy), [Research](https://today.umd.edu/topic/research)


**Units:** [College of Computer, Mathematical, and Natural Sciences](https://today.umd.edu/topic/college-computer-mathematical-and-natural-sciences)