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When the sky glows green on Mars

After the Sun sets on the Red Planet and temperatures fall below -62 degrees Celsius, part of its atmosphere begins to glow. It starts at an altitude of about 70 kilometers shortly after sunset. The spots, which are up to 1000 kilometers large and shine as brightly as the Northern Lights on Earth, then move at about 300 kilometers per hour across the night sky. Future astronauts, however, won’t be able to marvel at them, unfortunately, because the spectacle plays out only in the ultraviolet range, which is invisible to the human eye.

Researchers chose a green color for a false-color representation of the UV light intensity in images of the effect captured by the ESA probe, Mars Express. Thanks to data from NASA’s Maven probe, more is now known about the process and the source of the light.

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The last of its kind?

Stellar streams consist of groups of stars moving in orbit together. They are usually remnants of small galaxies that were absorbed by larger galaxies or former star clusters. The Phoenix stream discovered four years ago is the latter. It was, as researchers show in an article in Nature, once a globular cluster, and a very special one at that.

Globular clusters are special objects in themselves. Imagine the night sky full of gleaming stars shining much brighter than the brightest planets in our Solar System. The average distance between two stars of a globular cluster is only 0.1 light-years, while the closest star to the Sun is 4.5 light-years away. Every cubic parsec holds between 1000 to 10,000 stars (the stellar density in the vicinity of the Sun is around 0.14 stars per cubic parsec).

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Time travel in the quantum world: how to generate a self-healing reality

The “butterfly effect” is a term from nonlinear dynamics, which is a subdomain of physics. It occurs in systems that meet three requirements: the output is not always proportional to the input (“nonlinear”), the progression is dependent on time, but is a function of only the original state (“dynamic”), and randomness is not a factor (“deterministic”: if A, then B). When these three conditions are met, a small change to the initial conditions can lead to large changes in the results. The phrase was coined by the meteorologist Edward Lorenz, who was referring to a butterfly flapping its wings in the Amazon rainforest being able to influence the weather in Texas.

The phrase is generally used today when a seemingly insignificant cause can have a large effect. The quantum world does not exhibit deterministic behavior, however, so you can’t really speak of a butterfly effect there. There are, however, some parallels. Researchers are studying how quickly certain effects propagate in certain quantum systems. The most important effect here is decoherence, that is, the inevitable, but undesired disappearance of a fragile quantum state in favor of the normal world. To that end, you need to understand that quantum states unfortunately have the tendency to dissipate, primarily through interactions. This makes it difficult to build useful things like quantum computers, for example. The quantum state is ordered; decoherence spreads chaos, so this process is also called a “butterfly effect.”

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How many planets fit into a star’s habitable zone?

The habitable zone of our Solar System is relatively narrow. Mars is at the very outer edge of it, while Venus, which orbits closer to the Sun than Earth, is not quite inside it. Of eight planets, only the Earth is at just the right distance from its host star. A ratio like this would naturally lower the chances of finding inhabitable worlds in the universe. But is the Solar System an exception or the rule?

Astronomers have, in fact, found other star systems that give a rosier outlook. For instance, three planets are in the habitable zone of the red dwarf, Trappist-1. In a study in the Astronomical Journal, the astrobiologist Stephen Kane from the University of Colorado has determined what the maximum possible number of inhabitable planets could be. With his team, he tested models of a wide range of different planetary systems to find out how the members of these systems interacted with each other over billions of years.

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This star system will never be the Solar System

TYC 8998-760-1 might someday become something like our Sun. Right now, however, the young star is still a few billion years away from that. It’s been around for only about 17 million years. If it were the Sun, there would still be a long time before it would even be able to watch the dinosaurs. Nevertheless, the whippersnapper is still something special: astronomers using the European Southern Observatory’s (ESO) Very Large Telescope (VLT) photographed it and found two planets in its orbit.

“Even though astronomers have indirectly detected thousands of planets in our galaxy, only a tiny fraction of these exoplanets have been directly imaged,” says co-author Matthew Kenworthy, an associate professor at the University of Leiden, adding that “direct observations are important in the search for environments that might support life.” The direct imaging of two or more exoplanets around the star is even rarer; only two such systems had been directly observed before, both around stars that differ significantly from our Sun.

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Centaurs: they’ve been with us for a long time

We’ve been waiting for extraterrestrial visitors our whole lives – but in reality, they’re already here and have been with us for a long time. No, I don’t mean “Men in Black.” But it’s also not science fiction, it’s the truth. When astronomers discovered 2017 1I/ʻOumuamua, their surprise was enormous: we’d never seen an interstellar object inside our Solar System before. Or had we?

We had. For some time, astronomers have known about asteroids that don’t orbit the Sun in the same plane as the planets (the ecliptic), but instead on orbits that are at a greater or smaller angle to this plane. We know that the whole Solar System was made from a flat disk of dust and gas. Therefore, every object formed from that disk should also move within the plane of that flat disk. Unless, of course, some collision or gravitational interaction changed an object’s orbit at some point during the history of the Solar System.

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