2020
September
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Panspermia: colonies of bacteria can survive in interplanetary space

Deinococcus radiodurans is one tough bacterium. Neither the detonation of atom bombs nor the terrors of empty space bother it. But could it travel from planet to planet as a stowaway? Imagine microscopically small lifeforms being transported through space and landing on another planet. Bacteria that find suitable conditions for their survival on the new planet could then multiply and spawn life on the other side of the universe. This theory, which is known as “panspermia,” postulates that microbes could travel between planets and spread life throughout the universe. Panspermia has been debated for a long time, because it obviously requires that bacteria survive long trips in space, withstanding vacuum conditions, temperature fluctuations, and radiation.

“The origin of life on Earth is the greatest mystery of humankind. Scientists have taken completely opposite viewpoints on this topic. Some think that life is very rare and developed only once in the universe, while others believe that life can develop on any suitable planet. If panspermia is possible, life must be much more common than we thought before,” says Dr. Akihiko Yamagishi, professor at the University of Pharmacy and Life Sciences in Tokyo and lead researcher of the Tanpopo space mission.

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Milky Way vs. Andromeda: the collision has already begun

It’s inevitable that the Milky Way and the Andromeda Galaxy will one day collide and merge, even though right now there’s still 2.5 million light-years between them. Thus, the light that we see from Andromeda today was emitted from there 2.5 million years ago. The two most massive members of the Local Group are approaching each other at 120 kilometers per second. In three to four billion years (so while our Sun is still alive), up to 1.3 billion stars of the two galaxies will encounter each other. After another maybe three billion years, the merger will produce a gigantic elliptical galaxy, which could be called “Milkomeda” perhaps.

The merger, however, already began a long time ago, as researchers discovered using the Hubble space telescope. In an article published in the Astrophysical Journal, they describe how they studied the area around the actual galaxy, the so-called halo, through a program called AMIGA (Absorption Map of Ionized Gas in Andromeda). To do this, they examined light from 43 quasars – the extremely distant, bright nuclei of active galaxies powered by black holes – located far beyond Andromeda. The quasars are positioned behind different areas of the halo, so the researchers could study several different regions. By focusing on the light from the quasars through the halo, the team could observe how this light interacted with and was absorbed by the Andromeda halo and how this absorption changed in different regions. The immense Andromeda halo apparently consists of thin, ionized gas that does not emit any easily detectable radiation. Therefore, tracing the absorption of light coming from a background source is a better way to study these regions.

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More rogue planets than stars in the Milky Way?

When stars are born, their surroundings are not for the weak or squeamish. Planets have to find their way through a young system that has not yet reached a steady state. If they are unlucky, they will be swallowed up by larger planets – or flung out of the system entirely. Then they become lonely wanderers traversing the universe as ice-cold, rocky hunks that are very difficult to detect.

Nobody knows how many of these so-called “rogue planets” there are, because normal telescopes cannot detect their extremely low energy signatures. And they also can’t be discovered by means of transit events, like with normal exoplanets, because they aren’t orbiting a star.

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