The hunt for “earth twins”
Astronomers periodically report the discovery of potentially habitable exoplanets (planets outside the solar system) or even about “Earth twins”. It is the name given to planets whose gravity is comparable to Earth’s, have a solid, rocky surface, and whose temperature allows the existence of liquid water. The study of “Earth twins” is important not only for those who dream of colonizing space: Scientists hope to find the pattern of the origin of life in the Galaxy and how unique our existence is.
Actually, no one has ever seen planets similar to earth – Modern telescopes do not have sufficient capabilities for this. Scientists calculate the reality of their existence from indirect evidence by analyzing the light of the parent star. So you can learn about the planet through regular partial eclipses. (brightness drops), when it passes through the visible disk of the star. Based on this, it is possible to determine the orbit of the exoplanet and the conditions on it based on the brightness of the sun.
But it is possible to see a planet near an alien star. This was possible, for example, with the help of the Keck Observatory, which took many photographs of the movement of giant planets around the star HR 8799, 129 light-years from Earth. The Keck Observatory consists of two ten-meter telescopes combined into a single interferometer. (used to measure the difference in the path of two waves)This significantly increases their resolution. Maybe if you built a telescope several times larger, it would allow you to see small planets?
In fact, the problem is not only in the scope of optics and resolution. Planets are very faint spots in the sky near bright stars that “blind” the optics. To see them, the light of the star must be completely blocked, using a coronagraph device. The trace of its work is visible as a black dot in the center in images of HR 8799, but a coronagraph such as the Keck Observatory only allows one to see very large planets at a very great distance from the star (about the orbit of Uranus). ).
“Astronomers face similar problems when observing the solar corona, the weak hot plasma around the Sun. It is clearly visible during solar eclipses when the Moon, hundreds of thousands of kilometers away, acts as a natural coronagraph. Telescopes with a built-in, non-eclipsing coronagraph make it possible to observe the corona all year round, However, the quality of such images will be relatively poor and much worse than during the eclipse. For effective operation, the coronagraph must be placed away from the telescope.. Without such a device, it is almost impossible to see an Earth-like exoplanet, although the resolution of a telescope like the James Webb would be sufficient for this, “Lomonosov senior researcher from Moscow State University PK Sternberg State Institute of Astronomy and host of the Unearthly Podcast channel Gazeta. He told Ru » Vladimir Surdin.
Bigger is better?
There are various telescope projects created specifically to hunt for “Earth twins”. The most advanced of these is the American HabEx. (Habitable Exoplanet Observatory – Habitable Exoplanet Observatory) and its updated version HWO.
It is expected to have a four-meter diameter mirror that will be placed between the 2.4-meter Hubble and the 6.5-meter James Webb. Much more important than the diameter of the main mirror will be the presence of an external coronagraph. (sorcerer in Western terminology)tens of thousands of kilometers away from the telescope. Created from lightweight polymers, resembling a sunflower fifty meters in diameter, the oculator will need to be launched on a separate rocket and use engines to carefully adjust its position relative to the telescope so that it covers the star but not its planets. .
This project and others like it have not yet been approved and will definitely not be launched until 2030. However, even if HabEx could be implemented, the resolution would not be sufficient to see the details of the geography of the “Earth twin”. It will appear as a point of light, but even this result will be a major breakthrough for astronomers. For example, spectrometers will allow us to determine the exact composition of the atmosphere of such a planet, and if it is rich in oxygen, this will be a strong argument in favor of the existence of life.
Moreover, in astronomy, interpretation is no less important than the observations themselves. Yes researchers we are trying Develop a method to detect trees on the planet based on changes in their brightness throughout the day and year.
According to Surdin, seeing an exoplanet (such as its continents) in fine details is Requires a space telescope with an unrealistically large diameter, about one kilometer. It is unlikely that such a mass will be launched into space in the foreseeable future, but the astronomer offers two hypothetical options.
- The first is to use gravitational lensing. The sun’s gravity bends the rays’ paths like a giant lens, but to use it the telescope must be far away from the outer solar system.
- The second way out is to build a space interferometer, that is, several telescopes of the HabEx class, but spaced many kilometers apart and working together as a single multi-eyed instrument.
The edge of the universe and black holes
There is a simple principle in astronomy: the larger the diameter of the telescope lens (or the effective diameter of the interferometer), the better, and there are almost no theoretical limits to its capabilities. It may seem that if you make a cyclopean telescope, you will be able to see any rare object, even the edge of the Universe. Paradoxically, it is much easier to see than Earth-like exoplanets, and in some cases a giant telescope is of no use.
For example, in 2019, astronomers took images taken in the millimeter radio range of a supermassive black hole at the center of the Messier 87 galaxy (the constellation Virgo). In 2022, they “photographed” a black hole at the center of our Galaxy associated with the Sagittarius A* radio source. This has become the most important confirmation of Einstein’s General Theory of Relativity and modern theories of gravity, and it is necessary to obtain the highest quality image possible to clarify these theories and search for errors. A hypothetical telescope intended to search for continents on exoplanets could probably see Sagittarius A* in optical range, but that wouldn’t make much sense.
“It saw almost everything the same as a radio telescope, but it cost many times more. What we see is not the black hole itself, but the hot gas around it. It works approximately the same in the optical and radio range. Of course, the nuances of the image will be different, but not fundamentally,” Surdin explained.
When it comes to the edge of the universe, James Webb is already fulfilling this task. The Universe has no limit in the everyday sense of the word, but the observable Universe has a limit. Light moves at a constant speed, and the further away an object we observe, the younger it appears. By looking at a galaxy a billion light-years away from Earth, astronomers are literally looking back a billion years, observing the object at that age. It follows logically from this that, on the one hand, it is impossible to see an object whose light did not have time to reach us during the existence of the Universe, that is, 13.8 billion light years. On the other hand, this also means that you can see the first light sources on Earth.
This was James Webb’s most important mission and he completed it successfully. The telescope photographed galaxies formed 500 million years after the Big Bang. This immediately surprised scientists because they looked so old, but most likely astronomers were frustrated by the standard technique used to estimate the age of the galaxy.
However, they (or slightly older galaxies) can safely be considered the edge of the visible Universe. No matter how much we increase the resolution, we should observe absolute blackness behind them. If James Webb sees the existence of at least one light source that existed before the beginning of the Universe, this would require a serious revision of astrophysics theories.
However, by magnifying the James Webb telescope many times, it will probably be possible to see other elusive objects (Population 3 stars). Composed solely of hydrogen (the primary element) without heavy elements, these are what astronomers call the first stars in the Universe.
“A thirty-meter space telescope would make it possible to obtain spectra from individual star clusters in the first galaxies. In this way, we would be able to check whether their stars contain heavy elements. If not, then these are the first stars of the Universe,” Surdin said.
There is no need to image a single star, as the stars in the cluster must be approximately the same age.
Such supertelescope concepts all have one major limiting factor: money. The construction of James Webb cost the American budget $ 10 billion; This is comparable to the cost of a nuclear aircraft carrier, and a thirty-meter telescope will cost much more. With global military spending increasing, it seems unlikely that we will see many astronomical megaprojects implemented in the near future.