# JWST phase curve shows lava planet TOI-561 b reflects about 75% of starlight, pointing to silicate clouds

- Published: 2026-11-10 18:12 UTC
- Section: Sky & Space › Astronomy
- Tags: TOI-561 b, James Webb Space Telescope, lava planet atmosphere, phase curve, silicate clouds, exoplanet albedo, magma ocean, University of Waterloo, Lisa Dang
- URL: https://realtech.media/news/rt-520e65df393828af5e5877be_jwst_phase_curve/

**JWST observations of the lava planet TOI-561 b over 37 hours indicate an atmosphere, possibly with reflective silicate clouds on the dayside, according to the authors.**

![JWST phase curve shows lava planet TOI-561 b reflects about 75% of starlight, pointing to silicate clouds](https://realtech.media/media/2026/11/ba9dbbc5f9d67bc8.jpg)
*ESA, NASA, and L. Calcada (ESO for STScI), Wikimedia Commons, Public domain*

A team led by Lisa Dang, professor of physics and astronomy at the University of Waterloo, used the James Webb Space Telescope (JWST) to observe the rocky lava planet TOI-561 b for 37 hours, according to uwaterloo.ca. The observation covered nearly four complete orbits of the planet around its star. The authors report that a planet once thought too extreme to hold an atmosphere appears to have one, with a reflective layer of vaporized silicate clouds [1].

## Phase curve: brightness and heat over one orbit

The team measured how the planet's brightness and heat changed throughout its orbit, a technique known as a phase curve. According to the authors, it showed that the planet reflects a significant amount of starlight and that heat is redistributed around the planet instead of staying only on the sunlit side. Together, these point to an atmosphere [1].

An earlier study had found the dayside far cooler than expected for a bare, dark rock this close to its star. Webb data cited in the publication's retelling give about 1800 °C, against roughly 2700 °C expected without an atmosphere. The missing heat could be carried to the night side or reflected before the planet absorbed it. Observing the full orbit gave the first look at the night side, which always faces away from the star. It is not warm enough to account for the difference, so TOI-561 b must reflect roughly three-quarters of the starlight that hits it, comparable to Venus [1].

## Silicate clouds and the open question of composition

The team compared the observations with a computer simulation of the planet's climate. The simulation suggests that clouds of silicate minerals, including silicon dioxide (SiO2) and magnesium silicate (MgSiO3), could form on the dayside and act like sunscreen. By reflecting starlight and keeping the planet cooler, they may help it retain an atmosphere that would otherwise be stripped away [1]. The clouds themselves were not imaged: this is the explanation that fits the observations and modeling, not a confirmed fact.

The composition of the atmosphere remains unknown. It could be dense carbon dioxide, like a much hotter Venus, or rich in sulfur dioxide, a gas released from Jupiter's volcanic moon Io. The planet's surface is covered by an ocean of molten rock, which could act as a planet-wide volcano that keeps feeding the atmosphere [1].

Dang says the next question is whether the atmosphere resembles Venus or an extreme Io, and that observations at longer JWST wavelengths could help. The paper, with Samuel Boucher as first author, was published in The Astronomical Journal [1].

## Sources

1. [uwaterloo.ca](https://uwaterloo.ca/news/science/clouds-lava-planet-challenge-what-astronomers-expected)
2. [hi-news.ru](https://hi-news.ru/science/u-planety-s-okeanom-lavy-est-svoj-%c2%absolnczezashhitnyj-krem%c2%bb-kak-eto-vozmozhno.html)

---

Source: RealTech, realtech.media — https://realtech.media/news/rt-520e65df393828af5e5877be_jwst_phase_curve/