No one knows how big the icy core of Comet ATLAS (C/2019 Y4) might be--possibly no wider than a few kilometers. One thing's for sure, though, the comet's atmosphere is huge. New images from amateur astronomers around the world show that ATLAS's gaseous envelope has ballooned in diameter to ~720,000 km--about half as wide as the sun.

"Comet ATLAS's coma (atmosphere) is approximately 15 arcminutes in diameter," reports Michael Jäger of Weißenkirchen, Austria, who took the picture, above, on March 18th. "Its newly-formed tail is about the same size."

Other astronomers are getting similar results. 15 arcminutes = a quarter of a degree. Given Comet ATLAS's distance of 1.1 AU on March 18th, that angle corresponds to a physical size of 720,000 km.

On the scale of big things in the solar system, Comet ATLAS falls somewhere between the sun (1,392,000 km diameter) and Jupiter (139,820 km). It's not unusual for comets to grow so large. While their icy solid cores are typically mere kilometers in diameter, they can spew prodigious amounts of gas and dust into space, filling enormous volumes. In the fall of 2007, Comet 17P/Holmes partially exploded and, for a while, had an atmosphere even larger than the sun. The Great Comet of 1811 also had a sun-sized coma. Whether Comet ATLAS will eventually rival those behemoths of the past remains to be seen.

A team led by UC Riverside geologists has discovered the first ancestor on the family tree that contains most familiar animals today, including humans.

The tiny, wormlike creature, named Ikaria wariootia, is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut. The paper is published today in Proceedings of the National Academy of Sciences.

The earliest multicellular organisms, such as sponges and algal mats, had variable shapes. Collectively known as the Ediacaran Biota, this group contains the oldest fossils of complex, multicellular organisms. However, most of these are not directly related to animals around today, including lily pad-shaped creatures known as Dickinsonia that lack basic features of most animals, such as a mouth or gut.

The development of bilateral symmetry was a critical step in the evolution of animal life, giving organisms the ability to move purposefully and a common, yet successful way to organize their bodies. A multitude of animals, from worms to insects to dinosaurs to humans, are organized around this same basic bilaterian body plan.

From Jesus to "Jurassic Park," people dream of resurrection, cheating death, defying nature, and uncovering the mysteries of the past. We debate the ethics of reviving extinct species like the passenger pigeon or woolly mammoth, with scientists clamoring to make some poor, hairy proboscidean clone baby take its first awkward steps out onto the ice. Yet somehow, the idea of resurrecting long-lost plants never really caught on in the public imagination. Maybe that's because most people probably couldn't even name an extinct plant, let alone one they'd want to smell, see, or study, though Rachel Meyer, an assistant professor of ecology and evolutionary biology at the University of California, Santa Cruz, has a hard time picking just one.

She likes silphium, a mysterious herb prized by ancient Romans as a food, perfume, and aphrodisiac that, according to the BBC, was "overharvested and overgrazed" to extinction almost 2,000 years ago. But if she could actually resurrect any now-extinct flora, "I'd probably just opt to bring back some of the melon diversity that was lost," she told Gizmodo. She cites bygone melon varieties eaten by ancient Egyptians, and others that, according to legend, were so good a Renaissance-era pope died after overdosing on the sweet, pulpy fruit.

"There are a lot of delicious ancient things," Meyer said, "and I'm like 'man, how did we lose that?'" Meyer rhapsodizes about "eggplant varieties in ancient ayurvedic texts" and extinct varieties of carrots "of beautiful different colors, flavors, and aromas," used not just as food, but "in ceremony, and as medicines, and in embalming." There's a broad, storied slate of lost plant species and varieties "that have been sort of forgotten that maybe we want again," she said, and it's looking increasingly likely that "we could bring these things back."

True, an island of prehistoric ferns probably wouldn't have the same cinematic appeal as a T. rex, but in theory, the ability to bring a plant back from nonexistence could be a boon to conservationists, a way to restore long-lost wild biodiversity or traits that helped ancient crops endure harsh conditions. More than 99 percent of all species that have ever existed are now extinct, there has to be some good stuff hidden in the genetic compost pile — what might we find if we start pawing through botanical history for forgotten foods or medicines? Now, gene-editing technology and advances in recovering DNA have opened up the possibilities for plucking treasures from the past, but there are already a few cases in which humans have brought back plant life, ages after it completely disappeared from the planet.

String theory is perhaps the most controversial big idea in all of science today. On the one hand, it's a mathematically compelling framework that offers the potential to unify the Standard Model with General Relativity, providing a quantum description of gravity and providing deep insights into how we conceive of the entire Universe. On the other hand, its predictions are all over the map, untestable in practice, and require an enormous set of assumptions that are unsupported by an iota of scientific evidence.

For perhaps the last 35 years, string theory has been the dominant idea in theoretical particle physics, with more scientific papers arising from it than any other idea. And yet it has not produced even one testable prediction in all that time, leading many to decry that it hasn't even risen to the standard of science. String theory is simultaneously one of the best ideas in the entire history of theoretical physics and one of our greatest disappointments. Here's why.

Scientists have uncovered a splintered remnant of Earth's continental crust from millions of years ago, embedded in the isolated wilderness of northern Canada.

Baffin Island, located in between the Canadian mainland and Greenland, is a vast Arctic expanse covering over 500,000 square kilometres (almost 200,000 square miles), making it the fifth largest island in the world.

While the island comprises part of the newest recognised territory in Canada - Nunavut, formally established in 1999 - a new discovery shows this ancient landmass has undisclosed ties that stretch backwards in time so far, they actually emanate from a distant geologic eon.

While analysing igneous rock samples recovered from diamond exploration drilling in the Chidliak Kimberlite Province at the southern stretches of Baffin Island, researchers identified a mineral signature in the rock they had never expected to find.

Russia is creating the first ever topographic three dimensional map of the Moon to help decide where cosmonauts will land in future journeys to Earth's natural satellite.

The director of the Russian Space Research Institute Anatoly Petrukovich announced the plan on Sunday, saying the map will be created using stereo imaging and it will have a resolution of two to three meters.

"After the work of the American satellites, we have planar maps of the Lunar surface, but here, using stereo processing and light analysis, we will get a universal altitudes map of the entire Moon with high accuracy," he said.

Solar Minimum is not as quiet as you think. On March 20th, something exploded on the farside of the sun. The Solar and Heliospheric Observatory (SOHO) saw the debris flying over the sun's eastern limb:

China's Chang'e 4 mission has started its 16th lunar day of work on the far side of the moon, with the Yutu 2 rover beginning a journey in search of new areas.

Both the Chang'e 4 lander and the Yutu 2 rover and their science payloads are in good operating condition, despite the spacecraft spending over a year in the harsh conditions on the lunar surface.

Yutu 2 awoke on March 17 following sunrise over its position in Von Kármán Crater, with the lander following 16 hours later on Mar. 18, according to the China Lunar Exploration Program (CLEP).

The lander will continue its low-frequency radio astronomy observations, but a new plan has been formulated for the Yutu 2 rover, which has already provided insights into the composition of the surface and what lies below.

Watch video here.

Glass is anything that's rigid like a crystal, yet made of disordered molecules like a liquid. To understand why it exists, researchers are attempting to create the perfect, still-hypothetical "ideal glass."

In 2008, Miguel Ramos read in the newspaper that 110-million-year-old amber bearing pristine Mesozoic insects had been discovered a few hours' drive from Madrid, where he lived. A physicist who specializes in glass, Ramos had wanted for years to get his hands on ancient amber. He contacted the paleontologists working at the site, who invited him to visit.

"They provided me with the clear samples that are not good for them," he said. "They have no interesting insects or whatever ... but they are perfect for me."

Ramos spent the next several years intermittently working on measurements of the ancient glass. He hoped that the fossilized tree resin, after aging for so long, might approach a hypothetical form of matter known as ideal glass.

Like the Moon, some parts of Mercury are covered with craters where temperatures reach cold extremes. But the Earth's satellite has tiny amounts of ice, whereas on Mercury there is plenty of it. This mystery has made scientists wonder whether Mercury has received water in a way that couldn't work on the Moon. But if so - how?

Temperatures on Mercury can reach 400 degrees Celsius (750 degrees Fahrenheit), yet for some reason the closest planet to the Sun has vast amounts of ice. A new study conducted by researchers from the Georgia Institute of Technology seems to have cracked this mystery thanks to chemistry.

Solar winds that hit Mercury carry charged particles, including protons. Interacting with the planet's minerals, they generate so-called hydroxyl groups, which under extreme heat free up and smash into each other, producing water molecules and hydrogen. These molecules travel around the planet and some of them land in craters in permanently shadowed regions, areas, which never receive direct sunlight and have extremely cold temperatures.