Paul Sutter, astrophysicist
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The secrets hiding under Europa's ice

Jupiter's icy moon Europa. Photo: NASA / JPL-Caltech / SETI Institute

Europa, the second moon of Jupiter, is encased in a thick crust of ice. Sitting far from the Sun, it's one of the last places you would expect to harbor life. But due to its elliptical orbit around Jupiter — it periodically swings closer and further from the giant planet — the differences in gravity flex and squeeze the core, heating it to molten temperatures.

The end result: Buried under 100 kilometers of rock-hard ice is a globe-spanning liquid water ocean. More liquid water than on the Earth. But is there life?

Why it matters: New simulations suggest the icy shell is broken into segments that shift, flex, and subduct, just like the Earth's crust. Essential nutrients on the surface could then make their way to the ocean, providing a possible pathway for life —permanently locked away from sunlight — to survive.

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An interstellar interloper in the solar system

The path of A/2017 U1 as it passed through our inner solar system in September and October 2017. Credit: NASA / JPL

On October 19 astronomers with the Pan-STARRS facility in Hawaii spotted an otherwise unremarkable small object tumbling through our solar system, but initial and follow-up observations revealed several intriguing characteristics:

  • It was moving faster than 50,000 mph before it arrived, more than enough to ensure it wouldn't be captured by the sun.
  • It entered the inner solar system from an angle far steeper than other distant visitors like comets.
  • It appears to be more like an asteroid than a comet — if it were a comet, it would have produced a tail as it neared the sun.

Why it matters: All the evidence together suggests that A/2017 U1, as it's currently named, is not from around here. It likely formed in another stellar system altogether, was ejected who knows how long ago, and has been traveling interstellar space before a chance encounter with our sun. It's already on its way out — past the orbit of Mars — traveling back into the void.

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Prospecting for gold in the galactic wilderness

Gold nugget. Photo: studiocasper / iStock

The Earth formed over 4 billion years ago with a ready supply of heavy elements like gold and platinum, but the source of those elements has been somewhat of a mystery.

Stars like our sun fuse hydrogen into helium, and at the end of their lives go on to create carbon and oxygen before exhausting themselves. Bigger stars are capable of the intense pressures needed to make silicon, magnesium, nickel and iron before exploding in ferocious supernova detonations that can make even heavier stuff.

What's next: The recent observation of merging neutron stars puts an interesting twist on the game of elements: three Earth masses worth of gold was found in the remnants of that explosion. This means that, like supernovas, these energetic mergers are capable of forming heavy elements. Which process dominates in the universe? We're still not sure.

Go deeper: More on the neutron star collision.

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Universe's missing mass found hiding between galaxies

Johan Hidding / Flickr

We know how much total matter is in the universe, including "normal" matter (things like stars, planets, you, me) and more mysterious "dark" matter. However, only about 10% of the normal matter has been accounted for in surveys of galaxies. Astronomers have long suspected the missing matter sits in threads of gas between galaxies, but it's hard to detect because it's very tenuous.

What's new: Researchers now report spotting about 30% of the missing matter by looking for its shadow in the cosmic microwave background — the afterglow of the big bang itself. The background light filters through the gas and gets bumped up to higher energies through collisions with the hot particles, leading to a subtly higher observed temperature between galaxies.

Why it matters: While it doesn't completely solve the mystery of the missing matter, the research may help us paint a fuller family portrait of the universe. By understanding what it's made of, we can learn more about its past and future evolution.

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Astronomers find a giant, black, glowing exoplanet

WASP-12b compared to Jupiter. Image credit: Aldaron / Wikipedia

The extra-solar planet ("exoplanet") known as WASP-12b is perhaps the strangest world found yet. While known for almost a decade, astronomers recently observed it during an eclipse, allowing them to measure its reflectivity (or albedo) for the first time.

What they saw: Surprisingly, WASP-12b has only half the albedo of the Moon, and about 1/6th that of the Earth, meaning it reflects very little light.

It doesn't end there — the exoplanet is twice as large as Jupiter and orbits 16 times closer than Mercury does around the sun.This proximity heats WASP-12b to almost 5,000 degrees Fahrenheit, meaning that despite its blackness it glows deep red like a massive gaseous charcoal briquette.

The bottom line: The variety of worlds we're finding in the galaxy far surpasses even the wildest sci-fi stories, and is providing insight into the range of physics and chemistry in the universe.

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Our galaxy's giant black hole has a smaller sibling

NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)

By studying the motions of a particularly dense cloud of gas, astronomers have inferred the existence of a new black hole near the center of the Milky Way galaxy. It's not confirmed yet, but it's estimated to weigh in at a whopping 100,000 times the mass of our sun.

That's big, but not the biggest — that title goes to Sagittarius A*, a supermassive black hole sitting in the middle of our galaxy that has a mass 4 million times greater than our sun.

Why it matters: This "intermediate" class of black hole provides clues to the formation of their bigger cousins. It seems that every galaxy hosts a giant black hole. How do these black holes form and grow? What's the connection between giant black holes and the evolution of their host galaxies? Having a "missing link" in our own backyard helps answer those questions.

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Universe gossip: Colliding neutron stars detected

Rebecca Zisser / Axios

There are rumors within the astronomical community that LIGO, the super-advanced gravitational wave observatory, may have spotted the signature of two neutron stars colliding.

What they are: Neutron stars are the collapsed cores of massive stars, and are some of the most exotic objects in the universe. They can form in pairs that eventually collide and release massive amounts of energy. Those collisions also create subtle ripples in gravity that might have been detected by LIGO.

What's new: This specific event was seen with traditional telescopes, but it's the first time the same collision may have been detected from radiation and gravitational waves. The LIGO team is checking the validity of their results.

Why it matters: Much of our universe is hidden from us, and gravitational waves give us access to mysterious events. Vibrations from neutron star mergers, for example, can help us understand the origin of the universe's heaviest elements. Spacetime itself is ringing like a bell — we just need to listen.

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What planets need for life

Our expert voices conversation on "How to look for alien life."

We find ourselves in a universe that appears, at first glance, ripe for life. Liquid water, abundant even in our own solar system (though most of it is hiding underneath thick icy crusts), amino acids hitching rides on comets, simple proteins found in young systems, millions upon millions of stars exactly like our sun in just the Milky Way galaxy.

By all appearances we should not be alone, and yet we don't see a single sign of anybody else, anywhere.

The chances of life appearing in the universe are obviously greater than 0 (otherwise I wouldn't be writing this and you wouldn't be reading this), but seem far, far less than 1.

What Earth got right: We can understand why planets like Mars and Venus wound up dead — too small to sustain a protective magnetic field and choking on its own oppressive atmosphere, respectively — even though they had a decent shot. But we don't fully understand the special sauce that makes life possible. So we're playing a numbers game. How many planets are out there? How many have liquid water? How many have a stable star and the right cocktail for life? It's only by obsessive, detailed observations will we crack it.

The other voices in the conversation: