For thousands of years, humanity has been curious about the stars in our night sky. Planets, stars … perhaps even with intelligent life are all around us. And only in the last 25 years have we got the opportunity to know for sure the answer to this question, when we saw with our own eyes the first world outside our solar system. As telescopes developed, human ingenuity gave us new methods of studying the Universe - among which the most famous is the observation of the faint wiggle of a star, and later the method of planetary transit. The number of discovered exoplanets is growing by leaps and bounds.
The first planets seemed to be the easiest to find - massive giants too close to their parent stars. They were followed by less massive and more distant stars. To date, the Kepler telescope has already discovered thousands of solid worlds, of which 21 are similar to Earth and can be inhabited.
The idea that the Earth was rare and unique - a solid planet with the ingredients for life, located at the right distance from the sun to allow liquid water to exist - has quickly lost support over the past two decades. And the culmination of this process happened quite recently, on August 24, 2016, when scientists at the European Southern Observatory announced the discovery of a solid planet with a mass of 1.3 Earths, orbiting the closest star to us: Alpha Centauri. This world revolves around the parent star in 11 days, but the star itself has only 12% of the mass of the Sun and shines only 0.17% of the solar brightness. Yes, the red dwarf and the rocky planet have come together and may have made this world potentially habitable. But the funniest thing is not that a significant percentage of stars may have terrestrial planets close by, but thatthat almost everyone has them. May be.
Only from the orbital parameters that we measured, and the known laws of physics, we have extracted a tremendous amount of knowledge. This planet is almost certainly tidally locked at its star, that is, it is always facing the star with one hemisphere, like the Moon, which never turns to Earth with its "dark side". The star itself is actively and often spewing out flares. For the sun-facing side of the planet, this means disaster, but not for the dark side. And the "seasons" are determined by the ellipticity of the orbit, not the tilt of the axis. But this is very little information that we managed to get, and if we want to learn more about the planet, we will have to improve our technologies.
For example, we need to find out if there is oxygen in the planet's atmosphere. Or water vapor. Or carbon-rich signatures like methane and carbon dioxide. What about clouds? Are they thin or thick or not at all? What are they made of? Are they dark or do they reflect light? Could the atmosphere transfer heat to the dark side of the planet, or is the night side forever frozen?
If we can improve our resolution and perform spectroscopy on a direct imaging planet, these questions can be answered without ever leaving our own planet. This will require an extremely large ground-based telescope or network of telescopes. The 30-meter telescopes that are currently under construction are a big step in this direction, but reaching the planets near red dwarfs requires even more: huge telescopes with a diameter of 100 or even 200 meters are needed.
The composition of the planet's surface is quite another matter. If the clouds are transparent and the orbit is elliptical, there must be a "seasonal" difference between summer (when the world is closest to the star) and winter (when it is farthest) during Proxima's 11-day year b. Since the world is locked and not spinning (like most potentially habitable terrestrial planets near red dwarfs), there will be three climatic zones: scorching and fried along the star-facing hemisphere; frozen, ice-cold along the outer hemisphere and temperate zone in the middle. The planet may have continents and oceans, as well as a giant ice sheet on the night side. Or there may be heat transfer from the atmospheric planet and effective reflectivity, then the entire planet will have the same temperature. An example of such a development of events is Venus.
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If we can make direct observations of the light emitted by the planet - both visible and infrared - at different times in the orbit of the star, we could get answers to all of the above questions. In this we would be helped by giant telescopes with high light-gathering power and the ability to be fixed in the light of a star, preferably from space. The proposed LUVOIR space telescope with an accompanying umbrella could handle this. According to the plan, it is a 12-meter telescope (25 times faster than the Hubble telescope), equipped with a coronagraph. A little further away from it an umbrella will fly, blocking the light of the star and letting in the light of the planet. Although LUVOIR will not be ready until the 2030s, the umbrella could be built in the next five years, allowing us to visualize Proxima b using the methods we already have.
What kind of radiation does the planet emit? In addition to signals from reflected solar radiation, cosmic rays and the planet's own infrared heat, what else could be? For example, artificial signals on radio or other electromagnetic wavelengths? If these signals are sent by intelligent life, it's time to go and find it. This is the task of SETI, which is already seriously interested in the planet. We should also seriously think about it, since our radio broadcasting into space has decreased over the past 20 years, but electromagnetic signals remain. It is possible that the existence of artificial signals will spur us to seek artificial lighting on the night side of the planet.
Because our most cherished dream is to find signs of life, preferably intelligent. Biosignatures can be in a variety of forms: vapor of nitrogen, oxygen and water in the atmosphere; evidence of geotransformation or artificial lighting on the night side of the planet. All this can be seen from space. While we can investigate these signatures indirectly through atmospheric, surface and radiated signals, the best way to study the planet is to travel there ourselves. 4.24 light years may not seem so distant, but a Voyager 1 spacecraft traveling at 0.006% light speed will reach Proxima b in many thousands of years.
But other methods, using modern technology, would allow us to get there faster. The Breakthrough Starshot project proposes the use of space-based lasers to accelerate a spacecraft equipped with a sail. They could accelerate it to 20% the speed of light, and the entire journey would take some 21 years. A new source of fuel, for example, containing antimatter, as in science fiction stories, could very well become reality one day. If you accelerate along the way with constant acceleration, you could reach a star in 12 years.
In other words, taking into account the predicted technological progress and if we do not violate the laws of physics, we could send an unmanned spacecraft to the nearest Earth-like planet in the next thirty or forty years, and possibly robots or people. It's time to go, and if this discovery doesn't make us look for a second Earth, then nothing will make us.
ILYA KHEL
