China desires to put a small constellation of satellites in orbit across the moon to create a radio telescope that might open a “latest window” into the universe.
The array would consist of 1 “mother” satellite and eight mini “daughter” craft. The mother would process data and communicate with Earth, and the daughters would detect radio signals from the farthest reaches of the cosmos, Xuelei Chen, an astronomer on the China National Space Administration (CNSA), said at the Astronomy From the Moon conference held earlier this yr in London.
Putting such an array in orbit across the moon could be technically more feasible than constructing a telescope directly on the lunar surface, a enterprise that NASA and other space agencies are currently considering as certainly one of the following big steps in astronomy.
Related: Radio telescope on moon’s far side will peer into universe’s ‘Dark Ages’
“There are a number of benefits in doing this in orbit as a substitute of on the surface since it’s engineeringly much simpler,” Chen said throughout the conference. “There is no such thing as a need for landing and a deployment, and likewise since the lunar orbital period is 2 hours, we will use solar energy, which is way simpler than doing it on the lunar surface, which, if you would like to observe throughout the lunar night, then you might have to supply the energy for nearly 14 days.”
He added that this proposed “Discovering Sky on the Longest Wavelength,” or Hongmeng Project, could orbit the moon as early as 2026.
Why construct a lunar telescope?
A telescope on the moon, astronomers say, would allow them to finally see cosmic radiation in an element of the electromagnetic spectrum that’s inconceivable to review from Earth’s surface: radio waves longer than 33 feet (10 meters), or, in other words, those with frequencies below 30 megahertz (MHz).
“In the event you are looking into the low-frequency a part of the electromagnetic spectrum, you will find that, as a result of strong absorption [by Earth’s atmosphere], we all know little or no about [the region] below 30 megahertz,” Chen said. “It’s almost a blank a part of the electromagnetic spectrum. So we wish to open this last electromagnetic window of the universe.”
Astronomers are considering this a part of the electromagnetic spectrum for a superb reason. They think this sort of radiation might allow them to look into the so-called Dark Ages, the period of the primary few hundred million years after the universe‘s birth within the Big Bang.
At the moment, the fledgling universe was stuffed with an impenetrable fog of hydrogen atoms. Even when the primary stars began to form, their light couldn’t get through this haze at first. Astronomers know, nonetheless, that this atomic hydrogen itself emits a sort of signal generally known as the 21 centimeter line. A part of the microwave band of the electromagnetic spectrum, the 21 cm line has been helping astronomers track hydrogen clouds in our own galaxy, the Milky Way, because the Fifties, in line with astronomer Ian Crawford of University College London.
But when looking for the 21 cm line from the earliest epoch of the universe, astronomers must search for radiation with for much longer wavelengths. Because the redshift effect brought on by the accelerating expansion of the universe stretches electromagnetic radiation from sources moving away from us toward longer wavelengths, what was microwave radiation emitted by the hydrogen atoms throughout the earliest epoch of the universe today appears to observers on Earth as long radio waves. And that is precisely the sort of electromagnetic radiation that can’t be seen from the planet’s surface.
The moon’s far side, nonetheless, might be the most effective place within the solar system to search for this mysterious signal. Distant from Earth’s obstructive atmosphere, the moon’s far side can also be protected against man-made radio noise. In the course of the lunar night, it also faces away from the sun, which, too, is a strong source of radio waves. Astronomers say that the moon’s far side is, the truth is, probably the most radio-quiet place in the entire solar system.
A demo that did not quite work out
Since radio waves are the sort of electromagnetic radiation with the longest wavelengths, telescopes that may map their sources within the sky with high-enough resolution need to make use of multiple antennas distributed over a big area. China’s constellation would achieve that in space, with the satellites circling the moon in the identical orbit. The satellites would gather data while on the far side of the moon. The mother spacecraft would then relay the measurements to Earth when crossing the moon’s planet-facing side.
Chinese scientists have previously attempted to check this approach with two microsatellites called Longijang 1 and Longijang 2. The 2 spacecraft, also generally known as the “Discovering the Sky at Longest Wavelengths Pathfinder,” rode to the moon with the Chang’e 4 mission that landed on the lunar surface in 2019. Longijang 1, nonetheless, failed while entering the moon’s orbit, so astronomers only received data from Longijang 2. That probe’s measurements, Chen said, showed that the moon’s far side, indeed, is incredibly quiet.
“We did have the Longijang 2, which circled the moon for a while, and [its] spectrum shows that when the satellite enters the shadow of the moon or comes out of the shadow, you’ll be able to see where the radio interference appears and disappears,” Chen said. “It does show that the far side of the moon provides a super environment for this sort of measurements.”
Astronomers expect that they might discover way more than the signal of atomic hydrogen from the dark ages. A brand new, never-before-seen face of the universe is probably going going to spring into view once astronomers know easy methods to search for it. Magnetospheres of exoplanets outside the solar system could reveal themselves in long radio waves, and a few researchers hope that such an array could even perhaps allow us to make contact with intelligent extraterrestrial life.
“If we open up a brand new window, we are going to very likely see some latest interesting objects,” Chen concluded.
