THE UNIVERSE

Surprise! Pluto Has Dunes Made of Methane 'Sand'

Something weird is at work on the cold, dark plains of Pluto, where hundreds of regularly spaced ridges look a bit like an alien thumbprint pressed into extraterrestrial ice. Today, though, researchers report in the journal Science that the strange landscape is actually a dune field crafted from methane “sand.”
The observation is startling, given that scientists thought Pluto’s tenuous atmosphere wasn’t necessarily robust enough to support the formation of dunes, which by most definitions are sculpted by wind.

“Dunes on Pluto, or any other body, tell us there is a significant enough atmosphere to move materials around, and that there are particles to move—in this case, frozen methane sand,” says study coauthor Jani Radebaugh of Brigham Young University, who studies wind-sculpted landforms throughout the solar system and on Earth.

Scientists spotted the dunes in images from NASA’s New Horizons spacecraft, which visited Pluto in 2015. The pictures show methane mounds parked on the massive glacier that makes up the western half of Pluto’s “heart,” a region now called Sputnik Planitia. These pale, linear mounds sometimes stretch for more than 12 miles, and overall, they occupy an area that’s twice the size of Utah Lake. (Explore our first map of Pluto, featuring the formal names of features on the dwarf planet.)

The winds responsible for transporting that frozen sand into features resembling earthly dunes are likely blowing onto the glacial plain from the direction of a mountain range that rises along the heart’s border. These winds, which blow perpendicular to the piles of sand, have left dark streaks of material on Sputnik Planitia that allowed scientists to retrace their path.

source

How 1.7 Billion Stars Were Mapped With Dazzling 3-D Precision

The ESA's Gaia satellite is helping astronomers understand the origins of our galaxy, one star at a time.

More than a billion twinkling stars, drifting lazily across the sky as both Earth and our home galaxy revolve, have been mapped in 3-D by the European Space Agency’s Gaia satellite. On Wednesday, scientists released a massive catalogue of data from the ambitious project, the second such information dump so far. In it are details about the wanderings of nearly 1.7 billion stars, more than seven million of which have been determined with exquisite precision.

We’ve been waiting 20 years for this release,” says Amina Helmi of the Kapteyn Astronomical Institute at the University of Groningen.
Pinpointing the locations of stars on the sky may not seem like the most difficult task–after all, haven’t we been drawing the heavens since before writing was invented? But Gaia isn’t doing just that. It’s also making extremely precise measurements of the distances to those stars, which means that astronomers now have a treasure chest of information to open up and play with. Already, more than a dozen papers are set for publication in Astronomy & Astrophysics, astronomers are gathering at the FlatIron Institute in New York City to begin combing through the data, and teams are racing to pull nuggets of information from the data that could answer some crucial questions about the universe.

Source: NASA

My God, It’s Full of Stars! How do we know how far they are?

Launched in 2013, the Gaia satellite has been staring at the sky and multitasking like no telescope has ever done. One of its jobs is to measure the motions of stars, which astronomers can then use to geometrically determine how far away they are (the trick is getting those motions mapped with enough precision to enable the necessary mathematics, which Gaia’s keen eye can do). This data release contains the precise movements of 7 million stars in 3-D, and the 2-D motions on the sky for nearly 1.4 billion others. The team plans to release its final set of data in 2020, which will also include information about the distinct chemical signatures of those stars.

What was that you said about the expanding universe ?

Right. In addition to helping us understand a bit more about the galaxy we live in, the Gaia data will help scientists figure out how fast the local universe is flying apart. We’ve known since the 1990s that the rate of expansion is increasing, but the precise rate is still a bit fuzzy. Gaia will help scientists nail down a number called the Hubble constant, which is a measure of that expansion, by providing a beefy set of cosmic mile-markers that scientists can use to measure distances. For the local universe, these mile markers are Cepheid variable stars, which periodically pulse and share the same intrinsic brightness. (By comparing the observed brightness of distant Cepheids with their expected brightness, astronomers can figure out how far away they are.)

So far, astronomers have estimated those distances using data from 10 well-studied, long-period variable stars in the Milky Way. Gaia has increased that calibration sample size to more than 50, which means that teams can substantially improve their measurements of distances to local galaxies. From there, they can use Cepheids to build the next rung of the distance ladder, which relies on a particular type of stellar explosion called a Type 1a supernova that’s visible across billions of light-years.

“Establishing just how intrinsically bright Cepheids are is the key thing that Gaia will help us to achieve,” says David Jones of UC Santa Cruz. “Because we can then calibrate Cepheids and Type Ia supernovae, we have precise distances for much of the observable universe.”

Source : Nasa

Source

Is an Interstellar Asteroid Trapped Near Jupiter? Get the Facts.

The bizarre asteroid known as 2015 BZ509 is being touted as the first known interstellar visitor to stay in our solar system.

IF YOU COULD float above the plane of the solar system, you'd notice that more than 99.9 percent of the objects whirling around the sun orbit counter-clockwise, set into motion by the spinning disk of dust and gas that birthed our planets, asteroids, and comets.

But bizarrely, of the more than 779,000 known asteroids, at least 95 drive against our solar system's flow of traffic. Now, two researchers are making an intriguing, if controversial, claim: One of these unusual asteroids—2015 BZ509—goes backward because it was adopted from another star system entirely.

“When we started working, we did not want to know whether it was interstellar,” says Fathi Namouni, an astronomer with the Côte d'Azur Observatory. Instead, Namouni and Sao Paolo State University researcher Helena Morais have spent years studying objects that orbit our sun backward in the hope of unraveling how our solar system formed—a bit like trying to solve a murder by poring over the crime scene's weirdest blood spatters.

In a study published today in the Monthly Notices of the Royal Astronomical Society: Letters, Namouni and Morais argue that BZ509 joined our solar system in its infancy, settling into a backward yet stable orbit that travels in lockstep with Jupiter's path around the sun. In that case, they say, BZ509 could be a cousin of the interstellar asteroid 'Oumuamua, which zoomed through the solar system last year.

However, the study arrives at an interstellar origin for BZ509 by process of elimination—an approach that outside experts have criticized.

“It is very extreme—particularly since they don’t have any dynamic modeling approach—to support their ideas is by saying that everything else is impossible,” says Southwest Research Institute scientist Hal Levison, who wasn't involved with the new study.

Attack of the Clones

No one is denying that BZ509, or Bee-Zed for short, is one strange space rock.

Namouni and Morais took notice of the asteroid not only because it orbits the sun backward, but also because its orbit nearly overlaps with

Jupiter's—the first known object to play a game of chicken with our solar system's biggest planet. An orbital balancing act keeps Bee-Zed alive. Although Jupiter gravitationally tugs on the asteroid twice per 12-year orbit, the two tugs cancel each other out and stabilize the asteroid.

“It's like a truck going down a bumpy road, only it hits a bump, and it hits another bump that bounces it right back to where it should have been,” says Athabasca University astronomer Martin Connors, who wasn't involved with the new study.

Using computer simulations, Connors and his colleagues found in 2017 that Bee-Zed's orbit has been stable over the past million years. The discovery took Namouni and Morais by surprise; their previous work had suggested that orbits like BZ509's could only last 10,000 years or so.

To push these results further, Namouni and Morais built a model of our solar system in its current layout. They then sprinkled in a million virtual “clones” of Bee-Zed, each with a slightly tweaked version of the asteroid's observed orbit, and ran the simulation for the virtual equivalent of 4.5 billion years.

Source: Nasa

Many of the clones eventually collided with the sun or were ejected from the solar system. Half of them lasted less than seven million years. But 46 of the clones were stable over the lifetime of the solar system—and 27 of them closely resemble Bee-Zed's current loop.

For humans to have a statistical chance of seeing Bee-Zed, Namouni and Morais argue that the asteroid must have been in a highly stable orbit for 4.5 billion years. But if Bee-Zed has orbited the sun since the solar system's childhood, how did it end up going backward? After considering and rejecting a variety of potential explanations, they say it must be an interstellar interloper.

“We did not have any prejudices for any possible origin for this asteroid,” says Namouni. “We were quite surprised.”

Rogue One

Despite Namouni's confidence that Bee-Zed is interstellar, he and Morais haven't actually simulated the asteroid's capture from another star system. And in the absence of that analysis, other planetary science experts strongly disagree with the study's logic.

“The median lifetime [of BZ509's clones] is so short, I’d be looking for short-term solutions,” says Bill Bottke, also of the Southwest Research Institute.

Bottke and his colleague David Nesvorny suspect that BZ509 is actually an inactive comet from the Oort Cloud, a zone of icy debris on the far outskirts of the solar system. After being nudged long ago into a backward orbit, it could have entered its current loop just a few million years ago, they suggest.

After all, comets can definitely go backward; Halley's comet orbits the sun clockwise, just like Bee-Zed.

What's more, Namouni and Morais's own work suggests that wayward objects can more easily get stuck in Bee-Zed's particular orbit than in others. Models also show that the comet scenario can explain how other backward asteroids settled into place.

A New Hope

Resolving Bee-Zed's origins will require an immense amount of work. Levison, Bottke, and Nesvorny recommend running massive simulations of how the planets formed and ultimately settled into their current orbits, specifically to see whether local objects enter orbits like Bee-Zed's more or less frequently than interstellar ones like 'Oumuamua.