#planetary-accretion

#planetary-accretion

Discovered in December 2024, asteroid 2024 YR4 was briefly considered the most dangerous asteroid in decades after scientists initially estimated it had a 3.1% chance of colliding with the Earth in 2032. Closer observations quickly ruled out a city killer scenario, but instead astronomers calculated there was a 4.3% chance that the moon lay in the path of impact.

Since every planet spins at a different speed, the gears are built with different ratios: Earth takes about 24 hours to spin once, Mars takes about 24.6 hours, Jupiter spins much faster, and Saturn spins fast too. Because of this, each dial shows the real day cycle of that planet, so the clock doesn't calculate time digitally.

The new work was less notable for showing that we had found these bases in Ryugu than for solving a previous mystery: earlier studies had failed to detect them there, despite their presence in many other asteroid samples.

We found that life is more likely to survive an asteroid impact, so it's definitely still a real possibility that life on Earth could have come from Mars. Maybe we're Martians! The idea that life could have spread through the solar system or even the universe on rocks is known as the lithopanspermia hypothesis.

The population of super-Earths and sub-Neptunes, and the origin of the radius valley that separates these two classes of planets, is best explained by cores that are made of an Earth-like composition without a substantial amount of accreted ice8,9,10,11. For sub-Neptunes, the hydrogen-rich envelope overlies the rocky core for billions of years, whereas for super-Earths, the envelope may be retained for about 100 Myr (refs. ).

I think the first thing to remember is: We are right at the beginning of this adventure. There's so much excitement that every little signal - every "wiggle" in a spectrum - gets people saying, "Oh! That might be life!" And then, on the other side, other people respond with, "I don't see enough wiggles, so there's probably not even an atmosphere. Dead planet. Move on." Both reactions are too fast.

A dead star 730 light years away appears to be forming a powerful structure around itself - and despite their best efforts, astronomers aren't sure how. The cosmic corpse, designated RXJ0528+2838, is an incredibly dense stellar remnant known as a white dwarf, with a Sun-like star orbiting around it. This binary arrangement isn't uncommon throughout the universe, but what is strange is the structure surrounding the former body: a highly energetic and luminescent cloud known as a nebula,

Looking skyward fills us with wonder. Off-world, the Sun, planets, stars, and galaxies all await. Our Solar System encompasses our own cosmic backyard. Farther away, stars and star clusters abound within the Milky Way. Hundreds of billions of stars exist just within our home galaxy. Inside our Local Group, only Andromeda surpasses us in mass, size, and stars. More than 5 million light-years away, galaxies abound in groups and clusters.

A bright star in a nearby galaxy has essentially vanished. Astronomers believe that it died and collapsed in on itself, transforming into the eerie cosmic phenomenon known as a black hole. "It used to be one of the brightest stars in the Andromeda galaxy," says Kishalay De, an astronomer with Columbia University and the Flatiron Institute. "Today, it is nowhere to be seen, even with the most sensitive telescopes."

Plenty of asteroids can survive their fiery plunge through the Earth's atmosphere. If they're big enough, they can prove incredibly destructive, like the 60-foot Chelyabinsk meteor that exploded over the southern Ural region in Russia in 2013, releasing a blast equivalent to 30 times the energy of the atomic bomb that was dropped on Hiroshima. And in case an even larger space rock were to ever threaten humanity, we'd have to get creative to keep it from colliding with our planet.

NASA is quietly ending financial support for independent planetary science advisory groups, according to a letter posted to the agency's website on January 16. The affected groups have historically offered feedback to the space agency on science efforts ranging from the exploration of Mars and ocean worlds to the storage of extraterrestrial samples, and more. According to the letter, signed by Louise Prockter, director of NASA's Planetary Science Division, funding to support these Analysis and Assessment Groups will end toward the end of April 2026.

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