The researchers will be looking for habitable planets, but they emphasize that it is not an exit strategy:
– There is no planet B. If we find other habitable planets, we must emphasize that we will not move there.
That’s what the leader said Center for Planetary Habitability (PHAB) Trond Torsvik when the center was recently opened. He is a professor at the University of Oslo.
The goal, on the other hand, is to understand the conditions that enable life to arise and thrive. And maybe also find such planets.
Planets that orbit stars other than our own are called exoplanets. Today, about 5,500 such planets have been discovered. The first exoplanet was discovered by Didier Queloz and Michel Mayor in 1995. They received the Nobel Prize for it in 2019. Queloz was invited to the centre’s opening.
They must look for this
– The possibility of life on other planets has fascinated mankind for a long time. How did we get here and why are we here and are we alone? These are questions that we are trying to answer, but we are focusing on what makes a planet habitable, said Professor Stephanie Werner in a lecture at the opening.
When we look for habitability, it is in practice liquid water that we are looking for. That’s because we are mostly made of water.
Stephanie Werner
When researchers look for habitability, there is one factor in particular that is important, Werner said:
Whether there is liquid water on an exoplanet depends on the temperature, which in turn depends on several things: distance from the sun it orbits, the sun’s activity and size, atmosphere and activity in the exoplanet’s interior.
One of the things that has been studied is the so-called habitable zone. This is a given distance to the sun where there are comfortable conditions for life.
– Today the earth is in the habitable zone. What constitutes a habitable zone changes over time. Earlier it was Venus that was in the habitable zone. In the future it will be Mars. We know that habitability is time-dependent. It is therefore important to be able to say something about the age of the planet and the solar system, explains Werner.
Professor Stephanie Werner during her lecture when the PHAB center opened. (Photo: Elina Melteig)
The age of the exoplanets can become a nut, because the planets to be examined are very far away. Additionally, these solar systems may be different from ours. Therefore, it is not as easy to compare the processes that have formed the solar system.
We will look at observations of exoplanets and look at what we know about planetary evolution to understand what kind of atmosphere we can expect. Next, we will look at the habitability of the planet. How do we do it? We need the mass, the radius and the mass distribution in the planet, summarizes Werner.
A habitable planet should have an atmosphere
The atmosphere around Earth today makes it possible to sustain life here. It retains heat with the help of greenhouse gases and protects us from radiation.
In addition, our atmosphere consists of oxygen. It is important for multicellular organisms. Without oxygen, we might still be bacteria. However, the Earth’s atmosphere has not always been so hospitable.
Werner explains that the atmospheres around Venus, Earth and Mars were quite similar when the planets formed.
– The first atmosphere during planet formation may have been quite similar to the composition of the sun, i.e. consisting of hydrogen and helium. This atmosphere dissipated rather quickly. The next consisted of gases from volcanoes and magma oceans. It produced an atmosphere consisting mostly of CO2. After the appearance of cyanobacteria that invented photosynthesis, there was gradually more oxygen in the Earth’s atmosphere, explains Werner.
In addition, planets that are too hot or too cold can have atmospheres that “evaporate” or “freeze”:
– When we look at many of the planets that we think are too hot, we would not expect to see atmospheres. Then we have some planets that are so cold that the atmosphere should be condensed on the surface, says Werner.
When scientists are to understand the planet, it is important to understand what kind of atmosphere surrounds it and what things affect the atmosphere.
On Earth, it is life itself that has ensured that there is oxygen in the atmosphere, but there are other gases that can also be signs of life. One of them is the molecule phosphine.
It is not only oxygen and water that are signs of life
Phosphine has been found in the atmosphere on Venus, and it was speculated whether this could mean that there is or has been life there. On Earth, phosphine is produced by living organisms, but it turned out that the conditions on Venus are so different that it is possible for phosphine to occur without life as well.
Werner says that such discoveries often give rise to big headlines without necessarily needing to:
– We have an exoplanet with an atmosphere that we can observe. It is called K2-18 B. It was observed by the Hubble telescope. Then the headline was that this could be a super-earth that was habitable. A few years later, the planet was observed with the James Webb Space telescope with other instruments. Now we believe that this is hardly a super-Earth, but a hycean planet, says Werner.
That a planet is designated as a hycean planet means that it has an atmosphere containing hydrogen and that there is potentially liquid water there.
Could our magnetic field be the basis for life on Earth?
It has long been assumed that liquid water and atmosphere are a prerequisite for life. It is perhaps less well known that the magnetic field may have contributed to the Earth being a habitable planet.
In any case, that is one of the questions the researchers have asked themselves: What role does the magnetic field play? What is the role of the moon? And what role does the earth’s plate tectonics play?
It is believed that all these factors affect life on Earth, but it is unknown how much, and which of the factors are decisive. The researchers will therefore investigate how biodiversity on Earth has been affected over the past 750 million years.
– During this period, the earth has undergone drastic changes in climate. The Earth, for example, has been a snowball. We therefore wonder how these changes have affected biodiversity, Werner explains.
One of the ways to investigate which factors play which roles is to compare with other planets. Mars has a number of features in common with Earth:
– Mars has traces of liquid water because we have seen clay minerals and river deltas. We have also seen that Mars has had a magnetic field. We don’t know what happened, but the magnetic field disappeared. Then the atmosphere also disappeared. Mars may have had an environment that could have been suitable for life, but still ended up being an ice desert, explains Werner.
How to see a planet?
In addition to understanding how planets form and evolve, part of the problem is finding them.
Some planets can be seen directly, but then they must be very large and have a perfect angle to the telescope.
In addition, planets can be seen when they pass in front of their sun, but then they must also be at the right angle to the telescope – and this does not happen very often. To illustrate this, Werner included a picture of Venus:
– This is Venus in front of our sun in 2012. The next time we can see it from Earth is in 2117, so these are very rare events. We have to see it from the right angle to see it, she explains.
It is possible that there are many planets out there, but it is not certain that we can see them.
The most common ways to see planets is to measure changes in the star’s speed and changes in the light emitted from the star. Both the star’s movements and changes in light can be caused by planets.
The fact that there are many things that need to be done to see a planet may be the explanation for the fact that the first exoplanet was only confirmed about 30 years ago. Nobel Prize winner Didier Queloz explains the discovery as follows:
– We used a technique that wasn’t really supposed to work, but which turned out to work surprisingly well because there are so many planets, he said.
He further explains that what is even more fascinating is that there is no planet similar to Earth, with the same location as Earth.
– There is one good reason for that: It is that the technique we use cannot see such planets.
2023-11-11 03:30:00
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