NASA’s Pandora satellite has started science observations of at least 20 exoplanets, measuring their host stars so Webb’s atmospheric results can be read more reliably.
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Title: The Exozodi Spectral Effect: Residual Habitable Zone Dust May Bias exoEarth Characterization
Authors: Miles H. Currie et al.
First Author’s Institution: NASA Goddard Space Flight Center
Status: Published in AJ
Figure 1: Zodiacal light as seen from Cerro Paranal. [ESO/Y. Beletsky; CC BY 4.0]
This zodiacal dust is not exclusive to the solar system. Other star systems, such as Tau Ceti and Vega, have been found to host similar clouds of interplanetary dust. This means planets imaged in these systems will also have emission from this dust mixed into the light that we observe from the planets. The Habitable Worlds Observatory (HWO) is a future space telescope mission under development by NASA. One of its primary science goals is to directly image 25 Earth-like planets in the habitable zones of nearby stars and look for signs of life (or biosignatures) in these planets’ atmospheres. Exozodiacal dust (aka exozodi) represents the biggest source of astrophysical noise that will need to be subtracted out from HWO observations of exoEarths. The authors of today’s article look at the potential impact of exozodi emission on the spectra of exoEarth atmospheres.
Figure 2: Different models of three “zodis” of dust observed at an inclination of 60 degrees plotted across HWO’s potential wavelength range. The gray scattering model is shown in green, the solar system’s model is shown in black, with the red and blue debris disk models shown in their respective colors. The top panel shows the flux contrast between the dust and the star. The middle panel shows the flux per area. The bottom panel shows the total flux captured with a 7.2-meter HWO with the thin blue line representing the spectrum of an Earth twin 10 parsecs (33 light-years) away for comparison. [Currie et al. 2026]
The authors first assume four different models of exozodi dust and how the dust’s emission changes with wavelength. The first model assumes a dust cloud that acts as a gray scatterer, meaning the particles scatter all wavelengths of light with no preference, and the second model’s dust acts just like the solar system’s does. However, it’s unknown whether the composition of exozodi will be the same as the solar system’s. Therefore, they adopt two more models of exozodi that act just like debris disks that have different compositions. One model is bluer in color because it is made up of smaller particles that preferentially scatter blue light, and the other model is redder in color because it is made up of bigger dust particles or different chemical compositions. Each of these models over HWO’s wavelength range can be seen in Figure 2. The authors then simulate a modern Earth atmosphere (both clear and 50% cloudy) as well as an Archean Earth atmosphere to understand how different exozodi models will affect observations of different exoplanet atmosphere conditions and compositions.
In general, the effect that zodiacal dust has on the spectra of Earth-like planets can be broken down into two categories: its effect on the continuum and on the spectral features. The continuum is the object’s light emitted over all wavelengths and uninterrupted by spectral features. Spectral features are absorption and emission lines. These create either a dip or peak in the spectrum where atoms have either absorbed or emitted light at that particular wavelength. Lines at specific wavelengths tell us that a certain material is there, providing a list of possible chemicals that could be present in the planet’s atmosphere. For a brief summary of spectroscopy more generally, see here.
In the case of the continuum, exozodiacal emission raises the continuum, meaning the base flux of the planet is raised and absorption lines become more shallow. These effects can be seen in Figure 3, where the authors’ simulated spectra are plotted with and without zodiacal dust included. Not only is the continuum elevated for all models including zodiacal dust, notice how the dips become shallower at longer wavelengths. Because dust primarily radiates thermally, the red debris disk model nearly smooths out all dips beyond 1.25 microns! Molecules that absorb at these longer wavelengths, such as water or methane, may not be correctly identified with this type of exozodiacal emission.
Figure 3: Spectra of simulated modern-Earth atmospheres for clear (solid bright lines) and cloudy (solid dimmer lines) scenarios. The Archean Earth atmosphere is plotted in dotted gray. The redder exozodiacal spectrum has an elevated continuum and smoothed spectral features as opposed to the original, zodi-free spectrum plotted in black. [Currie et al. 2026, with annotations by Kaz Gary]
From Figure 3, the effects of zodiacal dust are minimized with a bluer zodiacal dust model. This means systems with “bluer” zodiacal dust may be more optimal for HWO observations, as bluer dust does not scatter as much starlight as gray, solar system–like, or red dust. From their results, the authors recommend that the residual exozodi-to-planet flux ratio (in the V-band wavelengths) be kept to less than 10-2 in order to correctly understand the line depths (identify if a molecule is present or not) and 10-3 in order to accurately retrieve molecular abundances (understand how much of a molecule is present in the atmosphere). Dust is pesky enough here on Earth, but to find life on another planet like ours, we’ll dust have to deal with it.
Original astrobite edited by Anavi Uppal.
About the author, Kaz Gary:
I am a fourth-year PhD candidate at The Ohio State University with a passion for planets. My current work focuses on modeling exoplanet observations for the Habitable Worlds Observatory and understanding planetary atmospheres. Outside of research, I help develop planetarium shows and love all forms of science communication. In my free time, I enjoy playing tabletop RPGs, painting, watching terrible reality TV, and hanging out with my pet hedgehog.
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The Moon may have emerged largely intact within hours of the colossal impact that shaped its birth. Earth has an unusually large moon for a planet of its size and position in the solar system, yet scientists still do not fully understand how that companion came to exist. Now, researchers from the Southwest Research Institute [...]
Given that it's the closest planet to the sun, Mercury seems like it should be the hottest planet in our solar system.
However, at a blistering 900 degrees Fahrenheit (480 degrees Celsius), Venus tops Mercury's 800 F (430 C) highest surface temperature, despite being an average of 31 million miles (50 million kilometers) farther from the sun. So how can the second planet from our star be hotter than the closest planet to it?
It all comes down to reflectivity, atmospheric composition and geological history, experts told Live Science.
A planet's distance from its star is not the only factor that influences the planet's temperature.
"Distance tells us how much sunlight arrives at a planet, but it does not tell us how much is reflected … absorbed, how efficiently heat escapes, or how effectively the atmosphere transports heat around the planet," Stephen Kane, an astrophysicist who studies planetary habitability at the University of California, Riverside, told Live Science in an email. "Those properties can be just as important as distance, and sometimes much more important."
Mercury makes the case in miniature. According to Kane, the planet has essentially no atmosphere, so incoming sunlight strikes bare rock directly, heating it to extreme temperatures during the day. But with barely anything overhead to trap that warmth, Mercury radiates it straight back into space the moment the sun sets. As a result, nighttime temperatures plunge from roughly 800 F (430 C) during the day to about minus 290 F (minus 180 C) at night — a swing of well over 1,000 degrees, he added.
Venus tells the opposite story. Wrapped in an atmosphere that's roughly 90 times as dense as Earth's and consists almost entirely of carbon dioxide, Venus traps heat so effectively that its surface temperature barely changes at all, no matter where the sun happens to be, Kane explained.
Sunlight arrives at a planet mostly as near-infrared radiation and visible light, which pass through atmospheres consisting primarily of gases such as nitrogen, oxygen and carbon dioxide with relatively little trouble. Once the ground and lower atmosphere absorb that energy, though, they re-release it as infrared radiation, the kind of energy we feel as heat. Carbon dioxide happens to be excellent at grabbing and holding on to infrared radiation, Kane noted.
On Venus, the atmosphere is so deep and loaded with carbon dioxide that infrared energy leaving the surface gets absorbed and re-emitted over and over before any of it finally escapes into space. Some of that energy gets redirected back downward, Kane said, further warming the planet's lower atmosphere and surface. However, the heat isn't trapped forever, since energy conservation means that Venus must eventually release the same amount of energy it absorbs.
Notably, Venus doesn't actually soak up more sunlight than Mercury overall. Thick cloud cover reflects roughly three-quarters of incoming sunlight back into space before it ever reaches the ground, and only about 3% of the sunlight that arrives at Venus makes it down to the surface, Kane said. In fact, if that atmosphere and cloud deck were stripped away, a bare-rock Venus would actually run cooler than Mercury, since it would be receiving only about 29% as much sunlight from the start, he explained. It's the blanket, not the sunbathing, that makes Venus the hotter world.
Venus' atmospheric blanket didn't spring into existence all at once, and how it formed is its own open question. Venus shows strong evidence of past and present volcanic and tectonic activity acting to smother the planet in greenhouse gases, Paul Byrne, a planetary scientist and associate professor of Earth, environmental and planetary sciences at Washington University in St. Louis, told Live Science in an email.
This volcanic activity has been so intense that Bryne describes modern Venus as sitting in a "post-runaway greenhouse" state, where its extreme heat has become a self-sustaining process regardless of what the planet's interior is doing at any given moment.
The heat isn't being generated from below; it's a consequence of the atmosphere Venus already has, locked in place by the same infrared-trapping effect described above.
Taken together, the experts' answers point to the same underlying lesson: How close a planet sits to its star is only the opening chapter of its climate story. What kind of atmosphere it has and how effectively that atmosphere holds on to heat are usually responsible for the rest.
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