Could aliens have detected the Earth using the radial velocity method?

People already know thousands of planets around other stars. We call them extrasolar planets or exoplanets, and to detect them, we have applied methods that may be within the reach of suspected extraterrestrial civilizations. Could an alien species with resources like ours have discovered or discovered the Earth?

Suppose they could know the radial velocity method. Will they find us?

“Hot Jupiters”

The first extrasolar planet around a normal star was discovered in 1995 and baffled the astronomical community.

The planet star 51 Pegasi opened the category of “hot Jupiters” as a gigantic and massive world (twice Jupiter’s diameter and twice its mass), but located about one-seventh of the distance from its star between Mercury and the Sun. One might expect that there will be large planets like Jupiter in the Universe, but no one expected them to be so close to their stars.

In these characteristics lies the key to its discovery.

An exoplanet is easier to find the larger it is (in diameter or mass) and the closer it is to its star. The planet of star 51 Pegasi is known today as Dimidio, and its star is called Helvetios.

Unlike that first hot Jupiter, Earth is a tiny world orbiting much farther away from the Sun. For a civilization with technology like ours, is detection possible?

blinding light

Direct detection of the Earth by reflected light is excluded. The orbits of any planets that may be around stars appear tiny when viewed from afar. This destroys the possibility of distinguishing the Earth by means like ours, if you want to do this by the radiation that it reflects, because it is lost in the glare of the Sun.

There are very few cases of exoplanet capture by direct reflected light under very favorable conditions and using sophisticated methods. But there is not the slightest possibility of finding the Earth with these resources through interstellar space.

The aliens are blinded by sunlight, so they have to resort to indirect methods.

Take, for example, the radial velocity that led to the discovery of Dimidius in 1995.

“Wah-view-view…”

Forget everything you learned in school, because it’s a lie that the earth revolves around the sun. We’re not going to tell you that the earth is flat (maybe we’ll save that surprise for another article), but we need to clarify that it is. it is not true that the Sun is in the center of the earth’s orbit, even at one of its foci, if we consider it an ellipse.

Classical physics teaches that both the Sun and the Earth move throughout the year, and both do so around the common center of mass of the system they make up.

Of course, the mass contrast between the Earth and the Sun is so huge that this “center of gravity” falls very close to the star, so much so that … it lies inside the Solar sphere! But the important thing is that it does not coincide with the center of the luminous star. Consequently, the Sun, having the Earth next to it, experiences a certain oscillation. This happens to any star with planets, and due to this effect, the first extrasolar planets were discovered, including Dimidium. The problem is that this reflex oscillation of stars occurs at negligible speeds.

The star Helvetius oscillates at over 200 kilometers per hour every four days in response to the pull of Demidius. This is not an astronomical speed, but by human standards it is more than significant. So much so that applied to a car would have been worth a more than well-deserved speeding ticket. The reflex speed of a star is reduced for distant planets and for light planets.

Consider examples of the solar system:

Mercury, despite its proximity to the Sun, is so light that it shakes the star at a speed of an insignificant millimeter per second. On the other hand, the record is held by Jupiter, which causes the Sun to reflexively move at over 12 meters per second, almost 60 kilometers per hour, at the speed of a moped on the road.

The reflex motion of the Sun at the expense of the Earth is only a third of a kilometer per hour: it does not reach ten centimeters per second.

Measure speed by color change

The Doppler effect is used to detect the reflex movement of stars endowed with planets. Starlight is broken down into its components and compared to a light source at rest, which reveals very small color changes in the radiation caused by the speed of the star in its periodic oscillation. This procedure requires very accurate measurements, repeated and distributed over a time interval several times longer than the planet’s orbital period.

Astronomy has reached the physical limit imposed by the excitation of the stellar photosphere itself, which gives the best accuracy of about one meter per second, just under 4 kilometers per hour.

As for the time it takes to detect a signal from the planet, a week of data collection may be enough for Demidius, but a minimum of two years of observations will be required to detect the Earth, and almost a year for Jupiter. a year, a quarter of a century.

Edge of the Impossible

Extremely smart, highly complex methods are being developed to increase the accuracy of the Doppler method to a threshold of several centimeters per second. It is hoped that this can be achieved with extremely large telescopes within the next few decades.

Thus, by the middle of the 21st century, the detection of planets like Earth around stars like the Sun may be on the verge of being possible. We might expect the same from an extraterrestrial civilization like ours.

Detecting the Earth with the radial velocity method would have been a very difficult technical achievement for aliens who were on par with humans in technological development, something on the verge of impossible.

The Doppler method has made it possible to detect planets that are similar in some aspects to the Earth, but always around stars much brighter than the Sun, since the same planet is capable of causing a more intense reflex oscillation if, other things being equal, it is next to a less massive star.

The Doppler method looks unpromising, too bordering on aliens. What can be said about other approaches? If we consider the possibility of finding the Earth from another planetary system by the method of transits, will they find us?

David Galadi Henriquez, Resident Astronomer, Calar Alto Observatory, Andalusian Institute of Astrophysics (IAA-CSIC)

This article was originally published on The Conversation. Read the original.

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