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An Ambitious New Technology Might be Needed to See Other Earths

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Sep 19, 2023, 12:57:24 PM9/19/23

How a starshade would reveal exoplanets. Credit: NASA/JPL

An Ambitious New Technology Might be Needed to See Other Earths
The race is on to discover truly habitable Earth-like worlds. While we
are starting to observe the atmospheres of large potentially habitable
planets such as Hycean worlds with the telescopes we currently have, the
most significant breakthroughs will likely come with the development of
advanced specialized telescopes. These new designs will likely use a
starshade to hide the glare of a star and allow us to directly observe
its exoplanets. But will that be enough to study distant terrestrial

Since the 1930s, astronomers have used various ways to remove glare from
a bright object to reveal fainter objects. For example, to reveal the
solar corona similar to what happens during a solar eclipse, astronomers
have used a coronagraph that precisely blocks the limb of the Sun within
a telescope. The idea was extended to look at large planets around
stars, where a small filter hides the starlight from view so that nearby
planets can be seen. However, these filters were generally placed within
the telescope itself, which limits the precision of the filter.

A starshade would remove the filter from the telescope and place it a
significant distance from the telescope itself. For a space telescope,
this means having two spacecraft, one for the telescope and one for the
shade. By placing the two thousands of kilometers apart, astronomers
would be able to see planets orbiting extremely close to their star.
This will be particularly useful for Earth-like worlds orbiting red
dwarf stars in their habitable zone, which are by far the most common
potentially habitable worlds.

One problem with this is that red dwarfs are much fainter than Sun-like
stars, and the starlight reflected off their planets is even more faint.
So even with an advanced starshade to block the starlight, the planets
may still be too faint to observe. But a new paper on the *arXiv* argues
that this problem could be solved thanks to an advanced type of optics
known as photonics.

Illustration of a hybrid photonic/coronagraph system. Credit: Desai, et al
While traditional optics can capture faint light, photonics works on the
scale of individual photons. One of its common uses today is in fiber
optic communication, so if you happen to have fiber internet, thank
photonics. In astronomy, photonics has been used for things such as
high-resolution spectroscopy and the detectors of some radio telescopes.

In this new paper, the authors describe ways that coronagraphs such as
starshades could be used in connection with photonic detectors, creating
a hybrid system capable of observing much fainter planets. For example,
light at the edge of a starshade could be focused by microlenses into a
bundle of fiber cables, which could then be routed to individual
photodetectors. The authors note that with careful design a telescope
could detect an optical contrast of more than 10 billion.

Starshade observatories such as the proposed Habitable Exoplanet
Observatory (HabEx) are still a long way off. It will likely be the
2040s before such a telescope could be launched. So there is plenty of
time for astronomical photonics to be developed and improved. But this
study shows it could revolutionize the way we see the Universe.

Reference: Desai, Niyati, et al. “Integrated photonic-based
coronagraphic systems for future space telescopes.” arXiv preprint
arXiv:2309.04925 (2023).

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One Reply to “An Ambitious New Technology Might be Needed to See Other
James Ryan
SEPTEMBER 19, 2023 AT 4:32 AM
” so if you happen to have fiber internet, thank photonics.” I only have
ADSL over copper (or aluminum?) wires, but I still thank photonics
because the entire backbone of the Internet relies on photonics. 🙂

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