Universe Today

September 13, 2023September 13, 2023 by Matt Williams

Whether Saturn's Rings are Young or Old, its Moons are as Ancient as the Planet Itself

The moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Some small moons are also shown. All to scale. Credit: NASA/JPL/Space Science Institute

Saturn is best known for two things: its iconic ring structures and its large system of natural satellites. Currently, 146 moons and moonlets have been discovered orbiting the ringed giant, 24 of which are regular satellites. These include the seven largest moons, Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, and Mimas, which are icy bodies believed to have interior oceans. In addition, there are unresolved questions about the age of these satellites, with some suspecting that they formed more recently (like Saturn’s rings, which are a few hundred million years old).

To address these questions, an international team of astronomers created a series of high-resolution simulations coupled with improved estimates of Trans-Neptunian Object (TNO) populations. This allowed them to construct a chronology of impacts for Saturn’s most heavily cratered regular satellites – Mimas, Enceladus, Tethys, Dione, and Rhea. This established age limits of 4.1 and 4.4 billion years for all five, with the two innermost moons appearing more youthful than the outer three. These results could have significant implications for our understanding of the formation and tidal evolution of moons in the outer Solar System.

September 13, 2023September 13, 2023 by Brian Koberlein

Has the First Biosignature Been Found on an Exoplanet?

Artist's impression of Earth in the early Archean with a purplish hydrosphere and coastal regions. Even in this early period, life flourished and was gaining complexity. Credit: Oleg Kuznetsov — Artist's impression of Earth in the early Archean with a purplish hydrosphere and coastal regions. Even in this early period, life flourished and was gaining complexity, and distant exoplanets might begin similarly. Credit: Oleg Kuznetsov

Recently I wrote about the discovery of a hycean world. A potentially habitable exoplanet with a deep warm ocean and thick, hydrogen-rich atmosphere. Such planets are thought to be somewhat common orbiting red dwarf stars, and they are an excellent candidate for life. While it’s an exciting discovery, buried in the research article was something even more exciting. Tentative evidence of a biosignature, hinting at the presence of life. You can guess which discovery started making headlines. But have astronomers really found life on another planet?

September 12, 2023September 13, 2023 by Carolyn Collins Petersen

Astronomers Observe Blobs of Dark Matter Down to a Scale of 30,000 Light-Years Across

Dark matter fluctuations in the lens system MG J0414+0534. The whitish blue color represents the gravitationally lensed images observed by ALMA. The calculated distribution of dark matter is shown in orange; brighter regions indicate higher concentrations of dark matter and dark orange regions indicate lower concentrations. (Credit: ALMA (ESO/NAOJ/NRAO), K. T. Inoue et al.?

Dark matter remains mysterious and… well… dark. While we don’t yet have a definite idea of what this cosmic “stuff” is made of, astronomers are learning more about its distribution throughout the Universe. Since we can’t see it directly, observers need to use indirect methods to detect it. One way is through gravitational lensing. Another is by looking for emissions from hydrogen gas associated with small-scale dark matter structures in the Universe.

September 12, 2023September 12, 2023 by Evan Gough

Lucy Has its First Asteroid Target in the Crosshairs

This image shows the tiny main-belt asteroid Dinkinesh. Lucy captured this image from 23 million km away. Image Credit: NASA/Goddard/SwRI/Johns Hopkins APL

NASA’s Lucy spacecraft launched almost one year ago, in October of 2021. Its journey is an ambitious one, and long. It’ll visit eight different asteroids in its planned 12-year mission. Two of them are main belt asteroids, and the other six are Jupiter Trojans, which share the gas giant’s orbit around the Sun.

Lucy’s first, and smallest, target asteroid is now in the spacecraft’s sights.

September 12, 2023September 12, 2023 by Evan Gough

The Hubble Imaged Some Globular Clusters in an Unusual Place: Near the Milky Way’s Centre

Most globular clusters are found in the Milky Way's halo. But some, like the glittering globular cluster Terzan 12, are near the galactic centre. Image Credit: ESA/Hubble & NASA, R. Cohen (Rutgers University)

Our galaxy has about 200 Globular Clusters (GCs,) and most of them are in the galaxy’s halo. Astronomers think most GCs were taken from dwarf galaxies and merged with the Milky Way due to the galaxy’s powerful gravity. That explains why so many of them are on the outskirts of the galaxy. But they’re not all in the halo. Some are towards the Milky Way’s galactic bulge. What are globular clusters doing there?

September 12, 2023September 12, 2023 by Brian Koberlein

Do The Gaps in Protoplanetary Disks Really Indicate Newly Forming Planets?

Artist depiction of a protoplanetary disk in which planets are forming. Credit: ESO/L. Calçada

Roughly 5 billion years ago Earth was in the process of forming. Gas and dust gathered with the young Sun’s protoplanetary disk, likely nudged a bit by the resonant gravitational pull of Jupiter and other large worlds. One can imagine that as Earth formed it swept its orbit clear of debris, leaving a gap in the disk visible from light years away. While we know this tale is reasonably accurate, the idea that planets such as Earth always clear gaps in a protoplanetary disk likely isn’t.

September 11, 2023September 22, 2023 by Evan Gough

JWST Accidentally Found 21 Brown Dwarfs

This artist's conception illustrates the brown dwarf named 2MASSJ22282889-431026, observed by NASA's Hubble and Spitzer space telescopes. Brown dwarfs are more massive and hotter than planets but lack the mass required to become stars. Image credit: NASA

When you launch humanity’s most powerful telescope, you expect results. The JWST has delivered excellent results by detecting ancient galaxies, identifying chemicals in exoplanet atmospheres, and peering into star-forming regions with more detail and clarity than any other telescope.

But every time a new telescope is about to enter service, astronomers tell us they’re excited not only about the expected results but also about the surprising results. And like other telescopes, the JWST has also delivered some surprises. While going about its business, the JWST has discovered 21 brown dwarfs.

September 11, 2023September 11, 2023 by Brian Koberlein

JWST Might Have Imaged a Hycean World for the First Time, With a Hydrogen-Rich Atmosphere and a Deep Planet-Wide Water Ocean

Artist depiction of the mini-Neptune K2-18 b. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)

Despite its great oceans, Earth is not really an ocean world. It has less water than icy moons such as Europa and Enceladus, a relatively thin nitrogen-rich atmosphere, and vast continents that rise above sea level. A true ocean world would have no continents, a warm sea hundreds of kilometers deep, and a thick hydrogen and water-rich atmosphere. They are known as hydrogen-ocean planets or hycean worlds. While we’ve long thought they exist, the James Webb Space Telescope may now have found one.

September 10, 2023September 10, 2023 by Matt Williams

Polaris is the Closest, Brightest Cepheid Variable. Very Recently, Something Changed.

View from within the Polaris triple star system; artist's rendering. The North Star is labeled Polaris A. Credit: NASA/ESA/HST, G. Bacon (STScI)

When you look up in the night sky and find your way to the North Star, you are looking at Polaris. Not only is it the brightest star in the Ursa Minor constellation (the Little Dipper), but its position relative to the north celestial pole (less than 1° away) makes it useful for orienteering and navigation. Since the age of modern astronomy, scientists have understood that the star is a binary system consisting of an F-type yellow supergiant (Polaris Aa) and a smaller main-sequence yellow dwarf (Polaris B). Further observations revealed that Polaris Aa is a classic Cepheid variable, a stellar class that pulses regularly.

For most of the 20th century, records indicate that the pulsation period has been increasing while the pulsation amplitude has been declining. But recently, this changed as the pulsation period started getting shorter while the amplitude of the velocity variations stopped increasing. According to a new study by Guillermo Torres, an astronomer with the Harvard & Smithsonian Center for Astrophysics (CfA), these behaviors could be attributed to long-term changes related to the binary nature of the system, where the two stars get closer to each other, and the secondary perturbs the atmosphere of the primary.

September 10, 2023September 10, 2023 by Brian Koberlein

The Closest Black Holes to Earth are Probably Hidden in This Nearby Star Cluster

The Hyades cluster, which is the closest star cluster to Earth. Credit: NASA, ESA, and STScI

In the constellation Taurus, there is a cluster of a few hundred stars known as the Hyades. The cluster is just 150 light-years away, and it could be harboring a stellar-mass black hole.