Circle vs. Rectangle: Searching for 'Earth 2.0' may be easier with new telescope shape

Engineers propose changing the way we observe planets outside our solar system and increasing the resolution, with the aim of identifying conditions on small planets, as well as finding the Earth equivalent.

By Prof. Heidi Newberg, Rensselaer Polytechnic Institute

Earth is the only known place where life exists, and all known life depends on liquid water to enable chemical reactions. Single-celled life has existed almost since the formation of the Earth, but it took about three billion years for multicellular life to emerge. Human life has existed for less than one ten-thousandth of the age of the Earth.

All of this suggests that life may be common on planets with liquid water, but that living things that explore the universe and aspire to travel through space—like us—may be rare. To find intelligent life beyond Earth, we may have to reach out to them.

A needle in a haystack

Observing an Earth-like planet separately from the star it orbits is a huge challenge for several reasons. First, the star is a million times brighter than the planet, making it difficult to detect the planet if both are blurred together. Second, according to lensing theory, the best resolution in a telescope depends on the size of the telescope and the wavelength of the light being observed. Planets with liquid water emit the most light at wavelengths of about 10 microns, and at this length the telescope would need to be at least 20 meters in size to separate the Earth from the Sun at a distance of 30 light years. Finally, the telescope must also operate in space because observing through the atmosphere would blur it too much. Currently, the largest space telescope is the 6.5-meter diameter James Webb Telescope, which is smaller than necessary.

Since deploying a 20-meter space telescope seems beyond the reach of current technology, scientists have explored alternatives. One involves launching several smaller telescopes that maintain extremely precise distances between each other, so that the entire array functions as one large-diameter telescope. But the required positioning precision—calibration on the order of the size of a typical molecule—is currently unattainable.

Other technological solutions include using shorter wavelength light, so that a smaller telescope can be used. However, in visible light, a sun-like star is more than 10 billion times brighter than Earth. We currently cannot filter out enough of the star's light to see the planet in this case, even if the resolution is sufficient in principle.

Another idea for blocking starlight involves flying a spacecraft called a “Starshade”—a structure tens of meters in diameter—tens of thousands of kilometers ahead of the telescope, so that it will precisely block the starlight while leaving the planet’s light unblocked. But this plan requires launching two spacecraft (a telescope and a Starshade). In addition, pointing the telescope at different stars would require moving the Starshade thousands of kilometers, consuming prohibitive amounts of fuel.

Rectangular perspective

The researchers offer a more practical alternative. They show that it is possible to find nearby Earth-like planets orbiting sun-like stars using a telescope similar in size to JWST, operating in the same near-infrared range (10 microns), but with a mirror that is a 1-by-20-meter rectangle instead of a 6.5-meter-diameter circle.

With a mirror of this shape and size, we could separate a star from a planet in a direction where the mirror is 20 meters long. To find planets at any angle to a star, the mirror could be rotated so that its long axis sometimes aligns with the line connecting the star and planet. We show that in principle this design could detect half of all Earth-like planets around Sun-like stars within 30 light-years—in less than three years. While this design will require further engineering and optimization before its capabilities are guaranteed, it does not have requirements that appear to require particularly difficult technological leaps, as do other leading ideas.

Further study of these planets could identify atmospheres that suggest life, such as the presence of oxygen produced by photosynthesis. For the most promising candidates, we could launch a probe to send back images of the surface. The oblong telescope could be a direct way to identify a planet similar to our own: an "Earth 2.0."

for the scientific article

More of the topic in Hayadan:

• A stunning image of the Red Rectangle Nebula revealed: it is not so rectangular but one of a kind
• Reducing the possibility of life on planets outside the solar system
• The tripartite venture to locate planets outside the solar system
• Blood Moon – Total Solar Eclipse Will Be Visible from Israel