June 17, 2024
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Discovery

The Habitable Worlds Observatory could see lunar and solar 'Exo-Eclipses'

A future space observatory could use exoeclipses to discover exomoon populations.

If you're like us, you're still coming down from the heavenly high that was last month. Total solar eclipse. The spectacle of the Moon blocking the Sun has also provided astronomers with unique scientific opportunities in the past, from the discovery of helium to the proof of general relativity. Now, eclipses in remote exoplanetary systems could help in the search for elusive exomoons.

TO recent study from the University of Michigan in partnership with Johns Hopkins APL and the Department of Physics and the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology titled Exomoons and Exorings with the Habitable Worlds Observatory I: On the detection of shadows and analog Earth-Moon eclipses seeks to use a future mission to search for eclipses, transits and occultations in distant systems.

Hunting for exomoons

“HWO will likely be able to detect exomoons using a variety of detection methods, unlike existing observatories,” said Mary Anne Limbach (University of Michigan), lead author of the study. Universe today. “In a system where we detect an exomoon through an exoeclipse, we could observe other signatures, such as moonlight within the spectrum of combined reflected light from the moon and the planet.”

The proposal Observatory of habitable worlds (HWO) was derived from the LUVOIR-B (Large Ultraviolet Infrared and Optical Explorer) concept. This was highlighted in the Astro2020 Decadal Study for space astronomy. HWO would operate from the Sun-Earth L2 Lagrange point (the current home of Euclid and JWST) and would launch on an SLS or Falcon Heavy sometime in the mid-2030s. HWO would employ a free-flying “star shield”, which would allow you to observe exoplanets that orbit stars directly. But what really attracts observers is the idea of ​​​​seeing large moons orbiting these planets. So far, the claims of exomoon detections as Kepler-1625b and Kepler-1708b have remained elusive. However, if these moons orbit along their respective ecliptic planes, we would see telltale dips in brightness as these moons pass into the planet's shadow and then cast their shadows back onto the primary host.

habex
HabEx and its free-flying star shield. Credit: NASA/JPL

Eclipses, Transits and Occultations

In astronomy, we call this eclipse transit pattern a series of mutual events, when one body passes in front of another. In our own solar system, Jupiter is a excellent example this. The Earth and Moon experience similar events twice a year during what are known as eclipse seasons.

Transits
Types of 'exo-eclipse' events in transit. Credit: University of Michigan.

“HWO's primary mission is to search for signs of life on planets orbiting other stars. To achieve this, HWO will need to observe many nearby star systems, sometimes for several days in a row,” says Limbach. “'During these observations, HWO will measure reflected light from directly imaged planets in the system. “If an exoeclipse (or transit) occurs during this time, we would observe significantly less light from the planet during the eclipse (up to about 30% less for an Earth-Moon analogue, depending on the orbital phase).”

We already have an idea of ​​what an 'exo-eclipse' or transit event would look like from a distance. In 2008, NASA repurposed the Deep Impact spacecraft for what became known as EPOXI (a combination of two acronyms: the Deep Impact Extended Investigation and Extrasolar Planet Observation and Characterization missions). looking back In the Earth-Moon system, EPOXI saw a series of transits. This gives researchers an idea of ​​what such an event might look like.

EPOXY
EPOXI sees the Moon transit the Earth. NASA/EPOXY

Searching for Earth analogues

The Habitable Worlds Observatory would work in the near-infrared, a band where large moons can eclipse their host worlds. With an Earth-Moon analog system, HWO is expected to see between 2 and 20 mutual events at a distance of 10 parsecs. The largest gas giant events could be detected at a distance of up to 20 parsecs.

“Given that HWO will have multiple exomoon detection methods and we predict that these will facilitate exomoon detection, HWO may be able to reveal general information about exomoons. as population, such as how common or rare large moons are around Earth-like planets, or the physical circumstances under which exomoons are easily found,” says Jacob Lustig-Yager (University of Washington). “If HWO is able to detect many exomoons, this could open the door to these types of population studies in the future.”

Without a doubt, the detection of exomoons through exo-eclipses will produce will be difficult. This will represent the cutting edge of what even the Habitable Worlds Observatory is capable of. This method will also have to deal with false signals. These include possible 'exo-rings' and even climate variability and rotation that change the albedo or overall brightness of the primary host. On the positive side, the researchers note that younger systems should produce more mutual events. Think about the Earth-Moon system early in its history, when the Moon was first torn away from the Earth and was much closer. This primordial Moon would have gained great importance in the sky, producing many eclipses.

A population of exomoons

“The next aspect we are investigating is the spectroscopic detectability of 'Earth-like' moons orbiting gas giant planets in the habitable zone,” says Limbach. “While these moons have often been photographed in popular culture (e.g., Endor and Pandora), HWO may be the first observatory capable of detecting and characterizing them, if they exist.”

Lucy
Another eclipse seen from afar. The total lunar eclipse of May 15-16, 2022, seen from 100 million kilometers away, courtesy of NASA's Lucy spacecraft. Credit: NASA

Ultimately, the methods described could lead to the detection of an entire population of exomoons, allowing us to say with some authority how common they are in the cosmos.

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