Move a star from its place how the Chinese space telescope will search for Earth 2.0

(ORDO NEWS) — A new orbiting telescope will help find habitable planets around stars similar to the Sun. Scientists from China have proposed a project for a space observatory that uses an unusual but effective way to search for Earth-like worlds.

You can find potentially habitable planets by literally watching them move their stars. Approximately this should be done by the orbital telescope, the project of which was proposed by Chinese astronomers.

This approach will work with planets that are elusive to other methods. In addition, it will help determine the mass of the exoplanet and learn something else important.

The project is called the Closeby Habitable Exoplanet Survey (CHES) , that is, “Survey of the nearest habitable planets.” NASA managers would definitely add one more word to make CHESS or CHEES. But in the Celestial Empire, apparently, they do not have a weakness for beautiful English abbreviations.

CHES aims to find Earth-mass planets around 100 sun-like stars. More precisely, we are talking about stars of classes F, G and K (slightly hotter than the Sun, just like the Sun and slightly colder than it, respectively).

All the selected stars are within ten parsecs (about 33 light-years), literally around the corner on a galactic scale.

Moreover, it is proposed to look for planets not just anywhere, but in habitable zones. A planet is said to be in the habitable zone of a star if the distance to the star allows the existence of liquid water.

Simply put, if the oceans do not evaporate under the local sun and freeze to the bottom, yearning for its mean rays.

The distance from a star to a planet is rigidly related to the period of revolution (thanks to the law of universal gravitation). The Earth revolves around the Sun in one year (unexpected news, right?).

If I were closer to the sun, I would cope faster. But then it would be too hot for life as we know it. So, if we are looking for Earth 2.0 around Sun 2.0, we should assume that one revolution will take about a year.

And this is bad news: after all, to be sure of the existence of an exoplanet, you need to detect several of its revolutions. Therefore, the authors of the project offer CHES to follow the accountable luminaries for five whole years.

Well, the goal is worth it. The search for life in the universe, like a man in a forest, must begin from the place where she was last seen. And we saw it on Earth, located in the habitable zone of the Sun.

How will CHES work if it gets launched, and why would it be able to do things that today’s planet hunters can’t? To understand, let’s talk first about the usual ways to search for exoplanets.

Move a star from its place how the Chinese space telescope will search for Earth 2 2
Scheme illustrating the transit method

Transit through the Universe

Astronomers know about five thousand exoplanets, and this figure is updated almost daily. There are many ways to search for distant worlds, but almost all discoveries have come from two of them.

Approximately 70% of the planets gave us the method of transits. Here’s how it works.

Let’s mentally draw a straight line from the telescope to the star – this, as professionals say, is the line of sight to the star.

And we still need this concept. Suppose the planet, making its regular round of the star, came between it and the observer.

In other words, she appeared on the line of sight. The planet will obscure some of the star’s light, so that the telescope will “see” that the star is slightly dimmed.

These, so to speak, microeclipses (transits) will be repeated on each revolution of the exoplanet around the star.

Let’s assume that the palmate scalefish from the planet Pluh are looking for planets near the Sun by the method of transits. Let them see the Earth’s orbit edge-on.

Then they were lucky: our planet periodically outshines the luminary for them. But it won’t be easy to notice. The Earth is quite small, so its transit through the direct “Sun-Splash” will reduce the brightness of our star observed by the plumes by only 0.008 percent.

It takes very good telescopes to isolate such a faint wink from the inevitable noise . For example, launched in 2019, HEOPS (how do you like it, planet Pluh?).

But after all, the orbit of the planet is not required to cross the line of sight to the star. Here are armored dragonflies from the planet Vzhuh looking at the Sun from the pole.

Well, Vzhuh is so unsuccessfully located. None of the worlds of the solar system will ever pass between the Sun and Wjuh. There will be no microeclipses of our star for Vzhuhan. Brothers in mind may think that the Sun has no planets at all.

We ourselves are constantly in the position of unlucky dragonflies. According to theorists, only about 10% of the planets in the Galaxy are so well oriented that they can be seen from the Earth using the transit method. The rest “pass below the radar”, or rather, past our line of sight to their stars.

Dancing with the Stars

The second important way to search for planets is the radial velocity method. On his account, about 20% of discoveries.

What is the point? Not only the planet is attracted to the star, but also the star to the planet. As the exoplanet circles its star in orbit, it also moves, as if dancing in place. In this periodic motion, the star either slightly approaches the observer’s telescope, then moves away from it.

Having studied the spectrum of the luminary, you can notice this movement and calculate its speed (for sophisticated readers, let’s clarify: thanks to the Doppler effect).

Let’s agree that the direction from us along the line of sight is “forward”, and in the opposite direction – “back”. It is clear that any movement of a star can be decomposed into three axes: forward-backward, up-down and left-right.

So, from the spectrum, we can only pull out the speed with which the star moves back and forth. That is, it shifts along our line of sight. Therefore, they speak of the method of radial velocities.

It is best if we see the planet’s orbit edge-on. Only two of the three velocity components remain: forward-backward and left-right. And at certain moments the star will only move back and forth.

It will move strictly along the line of sight, and all its speed will become radial. That is, our brothers ploppers, who see the solar system from the edge, again got lucky with geography.

How will they cope with the search for Earth? Our planet is not massive, so with its gravity, it gives the Sun a speed of only nine centimeters per second. To detect such a radial velocity, the pluhan technique must be five to ten times better than the Earth’s. And this is with their ideal location.

Now let’s imagine that the plane of the planet’s orbit is, say, at an angle of 30 degrees to the line of sight (that is, to our conditional horizontal). Under the influence of the planet’s gravity, the star will now move not only back and forth and left and right, but also up and down.

The speed of the star, already low, will be decomposed into three vectors instead of two. And the more “vertically” the orbit rises, the less “horizontal” radial velocity will remain.

So, what about our dragonflies, whose line of sight passes through the poles of the Sun? Alas, they will not notice any planets again.

Yes, the radial velocity method is not as demanding on the orientation of the orbit as the transit method. It can also detect a planet that does not cross the line of sight. But a movement almost perpendicular to this beam is too much. There, and radial velocity, consider, is not at all.

By the way, if the ray method is more universal than the transit method, why did it give us fewer discovered planets? For purely technical reasons.

Obtaining a qualitative spectrum of a star is much more difficult than measuring its brightness. So the “transiters” crush the “beamers” with the number of examined luminaries. But this is by the way.

Don’t think about microseconds

So, the two most mastered exoplanet search methods have a vast blind zone. These are planets whose orbits lie at a large angle to our line of sight to a certain star. The method of transits surrenders immediately: give it an eclipse! The radial velocity method is more universal, but too large angles are fatal for it.

But the CHES approach works great in the blind zone of both the transit and beam methods. Moreover, the unfortunate planet Vzhuh (this is where the dragonflies, we recall) is an ideal observation point for him to discover the Earth.

However, the ploppers would not be offended if they got a Chinese telescope: it will be able to discover planets in the line of sight.

What is this amazing method and why hasn’t it showered us with exoplanets yet?

This approach is called microsecond astrometry. Astrometry here is the determination of the coordinates of a star in the sky. And microseconds (angular) – the accuracy with which they are determined.

Let us recall what the radial velocity method is based on. On the fact that the star shifts slightly, succumbing to the attraction of its own planet. To hell with the spectra and the Doppler effect. Can we just see the luminary dancing in the sky?

Basically, yes we can. Only to determine the position of the star will have to be very, very accurate. Is the apparent displacement of the Sun caused by the gravity of the Earth large? When viewed from ten parsecs – 0.3 arc microseconds.

Achieving such accuracy is not an easy task. It is somewhat simplified if the displacement of a star is measured not relative to its average position, but relative to six or eight reference stars. These last must be “nailed to the sky.”

In other words, they are far enough from the Earth that any of their movements can be neglected. According to the calculations of Chinese scientists, a thousand parsecs is a suitable distance for such benchmarks.

But even this technique does not negate the fact that the telescope must be a miracle of technology. Moreover, highly specialized for their task, in contrast to universal tools such as Hubble or Webb.

Determining the positions of stars with microsecond precision is a very specific task that only a specially designed telescope can handle.

Here is the answer why the catalogs are still not full of “astrometric” exoplanets. Such observations simply do not have anything to perform. Except perhaps the space cartographer Gaia . For her, astrometry is her daily bread, her task is to determine the exact locations of the stars.

And Gaia (or, if you like, Gaia) has already discovered several exoplanets in the manner described above. But for her, this is a side effect: the goddess does not have time to stare at each star for five years, she needs to map the Galaxy. So potentially habitable worlds have to wait for their chance, or CHES.

Game and candles

There are no “dead” orbits for CHES. He, perhaps, will become the first tool to which you can give a list of stars and say: find all the potentially habitable planets there. This hunter won’t miss anything if he has enough time and accuracy.

In addition, the new telescope will help calculate the mass of the discovered planets. After all, the more massive the body, the more it shifts its star. This, incidentally, “can” and the method of radial velocities for those planets that are available to him.

Finally, CHES will be able to determine the exoplanet’s orbital inclination (the angle between the orbit and the star’s equator).

And this information is not available to either the radial velocity method or the transit method. Meanwhile, it should shed light on the laws of formation of planetary systems.

And yet, for an instrument comparable in technical complexity to Her Majesty Gaia, such tasks look too modest and highly specialized. It may seem to the layman that there is nothing more important and interesting than potentially habitable planets.

But professional astronomers have a different view of things. Gaia justified the effort (and a billion dollars) with a three-dimensional map of our region of the galaxy and the richest stellar catalog in history.

Whether experts will appreciate the importance of CHES as highly is an open question. So far, this is only a project, and no one has yet made a decision on its financing.


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