(ORDO NEWS) — It is not known when interstellar travel technologies will appear, or if they will appear at all. But the direction of the first such flight has already been determined: most likely, the destination will be Alpha Centauri, the closest star system to us. The light of the Sun reaches it in about four years, three months and three weeks.
This is one of the brightest stars in the southern sky, and the inhabitants of the Pacific Islands have used it for navigation since ancient times. However, even a relatively weak telescope allows you to see that the system includes two stars – the yellow Alpha Centauri A and the orange Alpha Centauri B, both slightly larger and brighter than the Sun.
Bound by gravity, they rotate in a fairly close neighborhood: the distance between the stars varies between 40-47 astronomical units (1 AU corresponds to the average radius of the earth’s orbit), and A and B complete a revolution in 80 of our years.
Planet: Proxima Centauri b
Value: 1.1 Earth radii, 1.3 Earth masses
Orbit: 0.05 Earth’s orbit
Period of circulation: 11.2 days
A little over a century ago, astronomers noticed that one of the stars in the vicinity of this pair moves in a very similar way to it. Further observations showed that it is gravitationally connected to the Alpha Centauri system, being its “younger component”.
The third star is located at a distance from the main pair, bypassing the tandem A and B with a period of about 550 thousand Earth years. Moving along an elongated orbit, it turns out to be closer to us for long periods of time than stars A and B. This is also indicated by her name – Proxima Centauri (Latin proxima – “nearest”).
Star: Proxima Centauri
Type: red dwarf
Dimensions and weight: 0.14 and 0.12 solar
Age: 4.85 billion years
Distance: 4.34 light years
Pale red dot
It is from the triple system of Alpha Centauri that alien invaders arrive on Earth, described in the main hit of modern Chinese science fiction – Liu Cixin’s novel “The Three-Body Problem”. However, real Centauri, if they exist, would hardly attack the Sun, because the neighboring system Luhman 16 AB is located 0.69 light years closer.
True, it consists of a pair of brown dwarfs, barely warm “failed stars”, but the inhabitants of the planet near Proxima Centauri should be accustomed to such a weak light. Their home star is a red dwarf about seven times smaller than the Sun and 33 times dimmer.
Because of this, the habitable zone – the region around the star where the temperature is quite moderate and liquid water can remain on the surface of the planet – is much smaller for Proxima Centauri than for the Sun. With us, it starts at 0.38 a. e. and ends at 10 a.m. e. from the star, covering the orbits of Venus, Earth and Mars.
The habitable zone of the red dwarf Proxima is much closer to its dim surface – between 0.04 and 0.08 AU. e. But possible future earthlings-migrants (and hypothetical Centauri) are lucky: this star just has a small planet lying at the right distance.
Its existence was finally established in 2016, after scientists from the European Southern Observatory (ESO) made a series of observations under the name “Pale Red Dot”. The name refers to one of the most famous space images, “Pale Blue Dot” – a photograph of the Earth taken by the Voyager 1 distant probe from a distance of about 6 billion km.
Proxima Centauri b is a planet slightly larger than ours, the closest to us and one of the most promising candidates for habitation. There is another planet in the star system, Proxima c, but it is too far away and looks more like an icy Neptune than Earth. The possible planet Proxima d is awaiting confirmation, in addition, the star may have an asteroid belt.
It is not surprising that the neighboring – and so diverse – system is of great interest. By cosmic standards, it is within easy reach, but for us these unfortunate four and a half light years are still an inaccessible distance.
The Voyager 1 probe mentioned above has only reached the edge of the solar system in the half century since its launch in 1977 and is located 23.3 billion km from Earth. This is equivalent to 21.5 light hours – let alone the 4.24 years that separate us from our neighbors. Nevertheless, it is possible that the first terrestrial probes will arrive at Proxima Centauri in our lifetime.
The Breakthrough Starshot project seems to be as incredible as it is authoritative. Among its founders are titans such as Stephen Hawking, Mark Zuckerberg and Yuri Milner, a Russian-born Israeli venture capitalist.
The board of trustees is chaired by renowned Harvard astrophysicist Avi Loeb, and the managing director is former head of NASA Ames Research Center Pete Warden, people who inspire respect and even awe. At the same time, the goal of the project is really fantastic: to send a flotilla of interstellar “ships” to Proxima Centauri in the coming decades.
Global look press
The miniature probes are even named appropriately – StarChips, “star chips”. It is assumed that a thousand of such devices weighing no more than 1 g will be delivered to a high orbit and thrown into free flight in a swarm. Here, the probes will deploy solar sails measuring 4×4 m. The ultra-thin foil will reflect the incident radiation, accelerating the flight, like a sail blown by the wind.
The impulse to the devices will be given by the beams of an array of lasers, which by this time should be working on Earth – somewhere in the mountains, above the densest layers of the atmosphere.
So StarChips will be able to gain up to 15-20% of the speed of light, and it will take them 20-30 years to fly to Proxima Centauri. Of course, some of the probes will inevitably die on the road, others will go astray, but at least a few out of a thousand will reach the target and be able to view the entire system from close up.
Using the same solar sails as antennas, they will send the data back to Earth, and four years later we will see what Proxima Centauri b and all its surroundings look like with a resolution of 20 megapixels. If, of course, everything goes according to plan.
Almost all the technologies needed for this already exist, but the problem is that each of them needs to be made orders of magnitude smaller and more efficient. The solar sail was demonstrated in action by the Japanese IKAROS mission, but now it needs to be reduced a thousand times.
Miniature uranium “atomic batteries” are used in some pacemakers, but for StarChips they must weigh a fraction of a gram – including a communications system, a microcomputer, ion thrusters for maneuvering and observation cameras.
The Breakthrough Initiatives website lists dozens of major technological challenges that need to be addressed to make such a flight possible. In the meantime, experts are struggling with them, there are other projects of this program.
The ultra-thin foil will reflect the radiation, speeding up the flight, like a sail inflated by the wind.
The Breakthrough Listen project is dedicated to the analysis of radio signals from about a million neighboring stars, which are registered by telescopes in the USA and Australia. At the end of 2020, scientists working at observatories reported finding a signal unlike a natural event, one of more than 4 million analyzed to date.
One can imagine how hearts beat when it turned out that the BLC1 candidate source is located in the vicinity of Proxima Centauri, and its Doppler shift corresponds to the orbital motion of the same planet b – as if it comes from somewhere in its orbit.
To doubt the habitability of Proxima Centauri b makes her own star.
BLC1 lasted for about 30 hours, in a narrow band at about 982,002 MHz, and did not repeat again. All this looked rather suspicious, and after a careful study of the signal, the scientists’ fears were confirmed.
Already in the fall of 2021, experts showed that a wave of a strange shape was the result of intermodulation – complex interactions that occur when several radio signals are superimposed on each other, in this case, signals from ground-based systems and orbiters, although it is not known from which ones.
Doubt the habitability of Proxima Centauri b makes her own star, a restless red dwarf. The exoplanet is within its habitable zone, 20 times closer to the star than the Earth is to the Sun. The flux of radiation here is about two-thirds of what our planet receives. Calculations show that the equilibrium temperature of Proxima Centauri b – about 234 K – is only slightly lower than that of the Earth.
However, the red dwarf flares up every now and then, showering the planet with ultraviolet and X-rays that can completely sterilize it. A powerful stellar wind and coronal ejection flows can easily carry away both the atmosphere and water from the surface: according to calculations, in just tens of millions of years the planet should be completely “naked”.
A strong magnetic field would help protect against such an impact, but whether Proxima Centauri b has it is unknown. In addition, at such a distance from the star, the planet most likely fell into the trap of tidal forces and is always turned to the star with the same side as the Moon to the Earth.
Because of this, its “daytime” hemisphere can become very hot, and the “nighttime” hemisphere can retain cosmic cold. Temperature differences can be softened by a heat-carrying atmosphere, but astronomers are also not sure about its presence.
Modeling the climate of Proxima Centauri b gives different results depending on many parameters: the speed of the planet’s rotation around its axis, the presence of water and its degree of salinity, the location of the continents, the density and composition of the atmosphere, etc. Life under such conditions is possible only in the sea.
Some studies show that Proxima Centauri b may be almost half water – according to some scientists, it is completely covered by an ocean 200 km deep. If aliens live here, then they do not look like the Centauri from the novel of a Chinese science fiction writer, but like Prul’s colleague, a reasonable and very quarrelsome octopus from the Soviet movie Through Hardships to the Stars.
Only the flight of the StarChips interstellar flotilla will help to finally make sure of this, but for now the nearest potentially habitable planet to us remains completely inaccessible.
An artist’s view of Proxima Centauri: the distant double Alpha Centauri is visible just above and beyond the bright disk of the parent star.
StarChip vehicles must carry everything they need for a long flight, including their own (probably nuclear) power source.
- Construction and cooling of ground laser array
- Solving the problem of scattering of rays in the atmosphere
- Accurately point probes in the right direction
- Saving the integrity of the sail with powerful radiation
- Impact of dust and other factors of the space environment
- Pointing cameras at the target, and transmitters – towards the Earth
- Sending data using a laser and a sail as an antenna
- Receiving and storing energy for the entire flight
- Political and ethical issues
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