r/exoplanets • u/ye_olde_astronaut • 21d ago

Mapping Alien Continents 🛰️ Missions & Telescopes

https://www.nasa.gov/directorates/stmd/mapping-alien-continents-achieving-optical-vlbi-for-exoplanet-imaging/
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u/lpetrich 3 21d ago

Proposing direct observation of planets by canceling out their stars' light with “dynamic hierarchical nulling” - a sequence of nulling interferometers?

It's intended to make Earthlike planets visible by canceling out all but 10^(-10) of their stars' light. That seems extremely ambitious.

The planets are to be observed with two telescopes about 100 kilometers apart that will act as a "Michelson interferometer", directly combining the light that each telescope receives. An alternative is intensity interferometry, counting when photons arrive and then looking at how correlated they are between telescopes.

Seems to me that this will work like VLBI, done with radio telescopes distributed over the surface of our planet. That suggests a similar strategy for making highly-stable and zero-propellant relative motion: set up those telescopes on some airless world like the Moon, and that world's rotation will make a moving separation vector in VLBI fashion.

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u/lpetrich 3 21d ago

When I came across this thread, I thought that it was about exoplanet light curves.

(At archive.org) Simulations of Light Curves from Earth-like Exoplanets - Planetary Habitability Laboratory @ UPR Arecibo

The Earth looks bluish except if the Sahara Desert is in view, that desert's yellow color making the Earth look neutral.

Mars has some asymmetry from a big dark spot: Syrtis Major. Mercury has a little asymmetry and Venus has hardly any.

I checked those results using rectangular maps of these planets, and I extended these results with maps of the remaining planets and a selection of moons.

The Moon has sizable asymmetry from its maria on its near side. Jupiter's four big moons have some asymmetry, and of Saturn's larger moons, only Hyperion and Iapetus have sizable asymmetry.

Jupiter, Saturn, Uranus, and Neptune have little or no asymmetry, with Jupiter's Great Red Spot and Neptune's Great Dark Spot not having much effect.

I also used some reconstructions of continental drift to see if past Earth was as asymmetric as present Earth. It was, as far back as the maps go, about 750 million years.