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Astronomie - The Infinite Possibilities in a Tiny Smudge From Outer Space

25.10.2022

Astronomers have captured a poignant view of another planetary system in the making.

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Mark McCaughrean and Sam Pearson of the European Space Agency / JWST / NASA / ESA / CSA
 

If alien astronomers observed our solar system from a distance 4.5 billion years ago, they would have seen a star surrounded by primordial gas and dust. That material, arranged in a narrow but dense disk, whirled round and round the young star. Over time, its particles collided and formed clumps. Gravity smoothed the jagged edges of the biggest ones to make planets and moons, and left the bits and pieces to become asteroids and comets.

The same process happens around other stars across the universe. We can even take a snapshot of it with the help of powerful telescopes. It doesn’t look like much, but that small, flying-saucer-looking thing in the image at the top of this article is a planetary system in the making. The little bright bulb in the darkness, encircled in its own ring of dust and gas, is known to astronomers as a protoplanetary disk. This is what our cosmic home looked like in the beginning, long before its star became known, to a bunch of life-forms on the third planet from the center, as the sun.

This work in progress is situated in the Orion Nebula, a luminous cloud of interstellar gas and dust about 1,500 light-years away. Its star is about 1 million years old—a baby, in astronomy terms. The dust around the star blocks the light from the bright nebula in the background, rendered here in gray, so the planetary disk appears in silhouette. The faint, fuzzy orb nestled within is not the star itself but rather starlight shining off the halo of dust around it, according to Mark McCaughrean, an astronomer and senior adviser for science and exploration at the European Space Agency. This is one of the most tantalizing environments in the cosmos, where small particles will eventually transform into full-blown worlds.

The image arrived earlier this fall from the new James Webb Space Telescope, which McCaughrean is using to study a cluster within the Orion Nebula that is home to many young stars like this one. “What we’re trying to look for is whether the particles in that disk have grown bigger than you would expect in the interstellar medium—average bits of dust, tiny things floating around in space,” McCaughrean told me. “Has this disk managed to actually get some of the particles to stick together and start the process toward planet building already?”

The Webb telescope can observe only the outermost edge of this disk, but any evidence of clumping there would suggest that the same process is occurring farther in, closer to the star, where the disk is even denser, McCaughrean said. According to planet-formation theories, gas giants like Jupiter and Saturn should already be taking shape here.

The star system, known by its coordinates as Orion 294-606, is not a new discovery, and astronomers have observed such targets before, in the Orion Nebula and elsewhere. They have found the telltale signs of planets taking shape by studying patterns in the flow of gas within a protoplanetary disk. Astronomers have even identified the distinct signatures of the chemical elements floating inside some of these disks, which allow them to make predictions about what future planets might be made of.

But there’s something poignant about the object that McCaughrean has captured, hovering in the shadow of a cosmic cloud. It reminds me of the “pale blue dot,” the famous image captured by NASA’s Voyager spacecraft in 1990 after its grand tour of the solar system, the one that inspired Carl Sagan to describe Earth as “a mote of dust suspended in a sunbeam.” When I first saw that image, I was kind of underwhelmed. It’s a flawed picture: The fuzzy streaks of sunlight are technical artifacts, something to do with the way the probe’s camera was pointed, and the tiny speck in the orange beam looks like something you’d try to wipe away on your laptop screen. Astronomy imagesoften have these problems—the subject and its significance are not always immediately clear. Only when you sit with the image for a bit, making room for wonder, do those pixels become something else. A grainy image can come to represent humankind’s attempt to understand the universe, and show us our place within it.

Orion 294-606 could be viewed as a zoomed-out, interstellar version of the pale blue dot. It’s not just because the image might evoke a sense of loneliness—though McCaughrean said that many other stars abound just out of frame—but because of the enormity contained within. The pale-blue-dot picture captured a whole world, and the Webb snapshot holds something even greater. This protoplanetary disk is about five times wider than our solar system out to Neptune. It likely has everything it needs to create a planetary system with as much variety as ours, to bring into existence its own versions of Jupiter and Saturn and maybe even Earth. That little smudge of pixels? It’s the kind of place that can create pale blue dots, and, perhaps, all the life that lies within.

Quelle: The Atlantic

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