Alpha Centauri A and B are only 4.37 light years away. Are there any planets near them? A life? Perhaps we can find out. Imagine that you are a few light years away, orbiting another star in our galaxy. If you look at our solar system from such a great distance, what should you see to determine the presence of life on one of our worlds? Even if the Earth were just one pixel in a telescope, you could still do it. By reflecting light from the Sun, you could directly see our world and understand that:
- there are oceans and continents on Earth;
- its color and reflectivity changes with the season when the plants bloom and are covered with snow;
- ice caps grow and shrink throughout the year;
- clouds form and dissipate;
- with the right tools, one would conclude that the atmosphere is composed of organic molecules that signal the presence of life.
If someone from a distance of several light years could do this with the Earth, it will be clear that we here on Earth can do it with another star. And if you're lucky, the nearest star system will have two ideal candidates: Alpha Centauri A and Alpha Centauri B.
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The Alpha Centauri system is a trinary star system. Alpha Centauri A is the same type as our Sun, Alpha Centauri B is slightly colder, and Proxima Centauri is an even colder red dwarf. Of course, Proxima Centauri is a little closer: 4.24 light years from us, not 4.37 light years. But Alpha Centauri A and B are much lighter and more suitable for life away from the parent star, and also easier to see. Any potentially habitable planets - solid worlds at the right distance - will be far enough from the star for a well-equipped telescope to see directly.
We usually think that our Sun is an "ordinary" star. But this is not entirely correct. Our Sun is more massive and brighter than 95% of the stars in our galaxy, and Alpha Centauri is 50% brighter. Even Alpha Centauri B, almost as bright as our Sun, is brighter than 90% of all stars. Because the two stars are so close and unusually bright, any potentially habitable worlds will be separated by a greater angular size from the parent star than other long-lived stars in the sky (that is, living for billions of years). So, if we look for potentially habitable planets near Alpha Centauri A and B, if we set such a scientific goal, we can do it with the help of a small and inexpensive, by astronomical standards, telescope.
The Hubble Space Telescope is 2.4 meters in diameter, and most telescopes that are designed to take pictures of planets directly from space should have diameters between four and twelve meters. The cost of such projects quickly skyrockets to billions or tens of billions of dollars. But from a scientific point of view, a telescope with a diameter of 45 centimeters will be enough, not only to look at the planets near the stars of Alpha Centauri, but also to find - if any - signs of the presence of an atmosphere, oceans, seasons and other aspects by which we are used to judging habitability. The next star like ours is 2.5 times further away, which means that you need at least a meter telescope in diameter.
The idea to create a small telescope like this that will go into space with a coronagraph blocking out the light of the parent stars has resulted in the proposed ACESat mission, which stands for Alpha Centauri Exoplanet Satellite. This telescope should be light, small, inexpensive, and at the same time highly capable: it will be able to find out if the nearest star has signals that we could connect with life.
This is a kind of high-risk, high-reward venture. Alpha Centauri A and B are a binary system of stars, which means that there are only three sure options to find a planet in this system:
- in a close orbit near Alpha Centauri A;
- in close orbit near Alpha Centauri B;
- in a far and wide orbit, away from both stars.
Either of the first two would be absolutely perfect for finding a solid, potentially inhabited world near a sun-like star. But if life is rarely found in a potentially habitable zone, or if there are no planets at all, then the scientific exhaust will be small. Unsurprisingly, a review committee at NASA raised concerns about the possibility of this “null result,” and partly because of this, the ACESat mission was not selected.
But NASA isn't the only way to launch a satellite into space. A similar mission can exist as a private funded enterprise - Project Blue. Logistics is easier than you might imagine. A 45 cm telescope is relatively cheap: you can buy it for tens of thousands of dollars. The tools will be complex, but not invaluable: millions of dollars will cost a coronagraph, new technology development, and instrument integration. And the mission goals can go beyond just looking at the nearest star systems.
The total cost of such a mission - including technology development, prototyping, testing, final design and launch - would be $ 50 million, significantly less than a typical NASA mission. Even if no planets exist, the development of coronagraph technology (with a deformable mirror), a new wavefront control algorithm and a new technique to improve speckle suppression will provide 500-1000 unique images of the same system, which will be incredible.
NASA's most successful planet-finding mission, Kepler, which has found more than 3,000 new exoplanets to date, was developed more than 20 years before its flight. It has since become our biggest revolution in how we understand stellar systems outside of our own, including a series of surprises. But Kepler can only identify planets that exhibit the rare and rigorous alignment geometry that allows planetary transit.
The beauty of Project Blue is that we have not yet been able to look at another star like the Sun in this manner, and when you look at new things in a new way, the possibilities for discovery are far beyond our imaginations. Crowdfunding may be required. We need the right investors and contracts. It can be one person or a consortium, but for a very small amount of money we can find out the answer to the most important question: are we alone in the Universe?
ILYA KHEL