Places in space where someone can see life on Earth

Is there life elsewhere in the universe? And if so, is there intelligent life that could detect us here on Earth?

– Where will we be space creatures? That was the question we asked ourselves, says Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University in Ithaca, New York.

So far, astronomers have found more than 4,700 planets in other stars. Some of them may have the necessary conditions for the development of life, because they are located in the so-called habitable zone, that is, at a reasonable distance from their star to obtain the right temperatures for liquid water. To find out if there really is life, scientists study the planet’s atmosphere for oxygen or other substances that are unmistakable signs of life. To find intelligent life and extraterrestrial civilizations, they look for signs of advanced technology, such as the strong signals of radio waves and light.

Lisa Kaltenegger and Jackie Fahrty of the Department of Astronomy at the American Museum of Natural History in New York wanted to discover if potential aliens in other stars in the Milky Way could examine the Earth in the same way.

Lisa Kaltenegger, Senior Lecturer in Astronomy, Director of the Carl Sagan Institute at Cornell University in Ithaca, New York.

Photo: Jason Kosky/Cornell Marketing Group

The most popular method Finding other solar systems with planets is to measure the brightness of a star. If it becomes weaker at regular intervals, this is a sign of one or more planets blocking some of the light as it passes in front of the star in its orbit around it. 70% of the planets that we know of have been discovered in this way.

Who sees the earth blocking some sunlight? Who are in such privileged locations where they can see the Earth passing in front of the sun? We wanted to find out, says Lisa Kaltenegger, and how it has also changed over time.

In the study published in the journal nature This week, Lisa Kaltenegger and Jackie Fahrty studied stars no more than 300 light-years away.

Light needs time to travel, and the closer something is, the brighter it gets. Then there’s more information in the spotlight, says Lisa Kaltenegger.

– Within 300 light years, we have found about 2,000 stars from which you can see Earth, either in the past, now or in the future.

Lisa Kaltenegger and Jackie Ferti searched for stars where the Earth may have been visible 5,000 years ago, around the time human civilization began to develop, even today and 5,000 years in the future. They found 313 stars from which Earth was visible before, 1402 stars where we can see us now and 319 more stars we will see later. 75 of the stars are so close to us that someone there could also be reached by radio signals sent from Earth in the past 100 years.

– We wanted to know how long the stars are in locations where you can see us. Everything moves in the universe. The Earth revolves around the Sun, and the Sun also revolves around the core of our galaxy. We found that most stars have been facing us for at least a thousand years, and a large percentage of them are more than 10,000 years old, says Lisa Kaltenegger.

The survey was made possible with the help of the 3D map of the Milky Way of the European satellite Gaia.

Gaia measures the exact locations of stars and how they move. To know where they are in the past and the future, we need to know exactly how they move. We can do that thanks to Gaia’s measurements, says Lisa Kaltenegger.

Map of the starry sky, seen from Earth, created by measurements of more than 1.8 billion stars, published December 3, 2020. Shows the brightness and color of light from stars spotted by the European Space Agency's Gaia satellite.  The brightest regions show regions in the sky with many bright stars.  The bright horizontal region is the plane of the Milky Way, where most of the galaxy's stars are located.  The two bright spots at the bottom right of the image are the Small and Large Magellanic Clouds, two small galaxies that orbit the Milky Way.

Map of the starry sky, seen from Earth, created by measurements of more than 1.8 billion stars, published December 3, 2020. Shows the brightness and color of light from stars spotted by the European Space Agency’s Gaia satellite. The brightest regions show regions in the sky with many bright stars. The bright horizontal region is the plane of the Milky Way, where most of the galaxy’s stars are located. The two bright spots at the bottom right of the image are the Small and Large Magellanic Clouds, two small galaxies that orbit the Milky Way.

Photo: ESA/Gaia/DPAC; A. Moitinho.

It’s only from a very small part The stars around us you can see.

There are over 300,000 stars within 300 light-years of Earth, so it’s a small percentage where you can see Earth passing by the Sun. It really makes sense, says Lisa Kaltenegger, when you consider the size of the Sun relative to the Earth.

The results are intriguing to those looking for signs of intelligent life in the universe.

– They can say: This sign comes from a star in which they may have seen us.

When the Earth passes in front of the Sun, it is also possible to check the materials in our atmosphere.

When sunlight is filtered through the atmosphere, it gets affected. If it has the right energy when it hits a molecule, the molecule can start to spin, or the electron in the atom can jump to a higher energy level. Then some of the light disappears. It would be like a fingerprint, Lisa Kaltenegger says, showing the materials in the atmosphere.

The James Webb Telescope, a space telescope developed by NASA, the European Space Agency and Canada, will be launched at the end of the year and will conduct such studies of planets in other stars.

– If there are planets in the habitable zone by the stars that we have identified, life may have arisen there. Lisa Kaltenegger says if there are aliens as curious as we are, and if they’ve developed a similar technology: they can then see that there is life on Earth.

The Gaia satellite creates a 3D map of our galaxy, the Milky Way.

The Gaia satellite creates a 3D map of our galaxy, the Milky Way.

Illustration: ESA-D. Docross

We already know That there are planets with conditions for life in some of the stars found by Lisa Kaltenegger and Jackie Fehrty.

Like the planet Ross 128b, if anyone was looking at us, they could have seen us 3,000 years ago, but they lost their position 900 years ago. So I wonder if they could detect intelligent life here, says Lisa Kaltenegger.

But there are other potential planets that we’ll soon see within sight.

Teegarden star has two planets in the habitable zone. From there you can begin to see us 29 years later. Another famous planetary system is found in Trappist-1, with seven Earth-like planets, four of which are in the habitable zone. But they won’t be able to see us until 1,600 years from now.

In the coming days, the US intelligence services will submit a report on UFOs to the US Congress.

Do you think people will associate it with your studies?

– I hope people will think our study is more interesting than the report, because as far as I know it doesn’t contain much. If you are really interested in whether there is extraterrestrial life, there is a very good scientific reason to explore planets, find planets with conditions suitable for life and so on. As for UFO sightings, it doesn’t interest me more than it would be a great shortcut to finding life in the universe without having to search for it, says Lisa Kaltenegger.

– But unfortunately we can’t just throw logic overboard. So we have to go the hard way, looking for planets in the stars after another.

What do you think we would do if we received a message from another planet?

– It’s a discussion that will be taken far above my salary level. But the United Nations actually has a Secretariat for Outer Space Affairs. I think there will be confusion and discussions, and hopefully we can agree on what we should do. But it’s hard to believe we could understand the message, if it came. It’s hard to communicate if you go to another country, and then we still have hands, mouth, and faces and we live on the same planet.

We can observe planets in other solar systems passing between us and their stars.  In the same way, objects on other planets can observe the Earth as the Earth passes over the solar disk.

We can observe planets in other solar systems passing between us and their stars. In the same way, objects on other planets can observe the Earth as the Earth passes over the solar disk.

Illustration: ESA

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