Why do astronomers look for signs of life on other planets based on what life is like on Earth?

Why do astronomers search for indicators of life on different planets based mostly on how life is on Earth? Couldn’t there be completely totally different sorts of life on different planets? – Henry, age 13, Somerville, Massachusetts

Have you ever ever performed hide-and-seek in a brand new place? It’s a lot tougher than taking part in at residence. You solely know the plain hiding spots: underneath the mattress, within the closet, behind the sofa. The trick is attempting to consider hiding spots you possibly can’t even think about. How do you search in locations you by no means thought could possibly be hiding spots?

That’s form of what scientists like me do once we search for alien life; we’re attempting to consider new methods to search for life. Within the meantime, we’re searching for life by searching for life like us as a result of that’s what we are able to think about.

Wanting close by

The closest place to search for extraterrestrial life is on planets inside our solar system.

NASA’s Viking 1 mission started orbiting Earth’s neighbor Mars again in 1976. In search of life on Mars was probably the most essential scientific questions for the mission. The spacecraft included a lander that would go to the planet’s floor to see if there have been any life-forms within the filth there.

Scientists knew that life on Mars could possibly be actually totally different from life on Earth, in order that they didn’t search for particular life-forms or molecules. As a substitute, they tried to design experiments to search for what life does, slightly than what it makes.

For instance, vegetation and another life-forms on Earth do photosynthesis, a course of that uses sunlight and carbon dioxide in the air to assemble power and develop. The Viking 1 scientists designed the lander to search for indicators of photosynthesis occurring on Mars.

To do this, the lander scooped up some filth, shined a lightweight on it and made measurements to see if any of the carbon dioxide within the air was transferred into the filth. This experiment didn’t present any indicators of photosynthesis in Mars’ filth.

The lander had two different experiments that seemed for proof of organisms rising within the filth on Mars. One used carbon dioxide fuel and one other one used sugar and amino acid molecules that life-forms on Earth prefer to eat.

The mix of those three experiments and different measurements led most scientists to agree that there most likely just isn’t life on the floor of Mars, no less than life that does one thing like photosynthesis or eats sugar. However we nonetheless don’t know if there are indicators of historic life-forms on Mars, and even present life deep beneath the floor.

The Viking lander experiments had been essentially the most direct exams for all times on different planets. When it comes to a sport of hide-and-seek, although, these experiments had been principally like trying within the closet: It’s a fairly apparent hiding spot, however it is best to test there simply in case. Even so, it took scientists a very long time to interpret the outcomes.

Wanting distant

In search of life exterior the solar system is even tougher and requires totally different methods.

The closest exoplanet – a planet orbiting a star that isn’t our Solar – is Proxima Centauri b, and it’s greater than 2 million, million miles (that’s 2 adopted by 13 zeros) away from Earth. These distant worlds are so far away that scientists are usually not going to ship landers to do experiments on them for a very long time.

In search of life on exoplanets is form of like attempting to play hide-and-seek in your neighbor’s home, however you solely get to look by way of the home windows and might’t go inside. You may get fortunate and get simply the suitable angle to identify somebody hiding, however you possibly can’t know all of the spots you’re not in a position to see.

Instruments like the brand new James Webb Space Telescope can reveal the scale of exoplanets, how shut they’re to their stars, and possibly the gases of their atmospheres. However that’s it. How would you search for life with that?

Astronomers have considered searching for life on exoplanets by looking for oxygen. They began with this technique as a result of on Earth, life-forms made a lot of the oxygen in our environment. Possibly oxygen on one other planet was made by alien life.

We’ve discovered, although, that there are different methods to make oxygen that don’t contain life. So now, astronomers don’t search for simply oxygen – as an alternative they’re on the hunt for a planet that has oxygen together with water and different gases, like methane and carbon dioxide. Collectively, these mixtures may point out life as a result of we don’t assume planets with out life would have them. However we’re nonetheless unsure about that, too!

In search of life by searching for these gases is form of like trying behind the sofa in our hide-and-seek sport. Do we all know anybody goes to be there? No. However we solely get to look by way of the home windows, and we are able to think about individuals hiding behind couches. We would as nicely attempt – the place else would we even look?

What sport are we taking part in?

There are two large variations between taking part in hide-and-seek and searching for aliens.

First, while you’re taking part in hide-and-seek, you normally know that you just’re taking part in with another person. We do not know if there are aliens on the market to search out! It’s attainable there’s no different life on the market, and it’s attainable there are aliens proper subsequent door. Till we discover examples of life apart from our personal, we gained’t know the way frequent life is within the universe.

The second distinction is that almost all scientists don’t assume alien life is hiding from us; it’s simply that we haven’t noticed it but. There are some concepts that extra superior civilizations might avoid being detected, however researchers don’t assume that’s occurring in our solar system.

Most astronomers and astrobiologists know that if we solely search for life that’s like Earth life, we would miss the indicators of aliens which can be actually totally different. However actually, we’ve by no means detected aliens earlier than, so it’s onerous to know the place to begin. While you don’t know what to do, beginning someplace is normally higher than nowhere.

In search of life utilizing experiments just like the Viking lander or looking for oxygen won’t assist. However we would get fortunate. And even when we’re not, we’ll get to cross a few apparent potentialities off the listing. Then we are able to give attention to the tougher query of imagining one thing we’ve by no means considered earlier than.

The writer is an Assistant Professor of Complicated Adaptive Programs, Arizona State College

This text was first printed on The Conversation. It’s republished right here underneath a Inventive Commons license.