Blog Archives

Rhea Eclipses Dione While Cassini Watches

Saturn's moons Rhea (front) and Dione (back) pass each other on Oct. 11, 2015. (NASA/JPL-Caltech/SSI/Jason Major)

Saturn’s moons Rhea (front) and Dione (back) pass each other on Oct. 11, 2015. (NASA/JPL-Caltech/SSI/Jason Major)

It’s been a while since I last made one of these: it’s an animation comprising 27 images acquired by Cassini in various color channels on October 11, 2015. It shows Saturn’s second-largest moon Rhea passing in front of the smaller and more distant* Dione, both partially illuminated by sunlight. I cleaned up some image artifacts from each frame and adjusted the levels to make the blacks black and not banded, like is often found in images like these. I also added a bit of a glow to the moons, to enhance the sense of light (and bring out some of the detail in the darker areas.)

There’s nothing particularly scientific here, just an enjoyment of the endless and ongoing dance of the spheres!

Check out an older moon animation of Rhea here.

*Dione is more distant from the Cassini spacecraft in these views; it’s actually closer to Saturn in its orbit than Rhea.

Dawn Finds Similarities Between Ceres and Saturn’s Moons

Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. (Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.)

Ceres (left, Dawn image) compared to Tethys (right, Cassini image) at comparative scale sizes. (Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA and NASA/JPL-Caltech/SSI. Comparison by J. Major.)

Around 600 miles wide, covered in craters and cliffs, a composition of rock and water ice… these are descriptions of both several of Saturn’s moons and the dwarf planet Ceres, based on recent observations by NASA’s Dawn spacecraft. New topographical maps show that, in terms of surface features anyway, Ceres shares similarities with Saturn’s icy satellites.

“The craters we find on Ceres, in terms of their depth and diameter, are very similar to what we see on Dione and Tethys, two icy satellites of Saturn that are about the same size and density as Ceres,” said Paul Schenk,  Dawn science team member and a geologist at the Lunar and Planetary Institute (LPI) in Houston, TX. “The features are pretty consistent with an ice-rich crust.”

Read more in my article on Universe Today.

Are You Ready For Pluto?

Pluto and Charon as seen by New Horizons' LORRI camera on June 25, 2015

Pluto and Charon as seen by New Horizons’ LORRI camera on June 25, 2015 (NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)

New Horizons sure is! With just over two weeks to go before the first-ever (and I repeat: EVER!) visit to Pluto and its family of moons the excitement has really ramped up exponentially, especially considering the increasingly detailed views of Pluto and Charon that the spacecraft has been capturing on approach. No longer just a couple of bright pixels against a background of stars, the two worlds now show actual detail that can be easily discerned. In other words, things are getting REAL!

It’s only going to be getting better from here – and quickly. As Principal Investigator Dr. Alan Stern said, “There’s only one Pluto flyby planned in all of history, and it’s happening next month!”

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Water Water Everywhere

Earth isn't the only planet with water – we just need to know where to look.

Earth isn’t the only planet with water – we just need to know where to look.

Everyone knows that Earth is a “water-world,” with oceans covering 71% of its surface and at least as much contained within our planet’s mantle deep below its crust. But there’s also liquid water to be found elsewhere in the Solar System: on Mars, on the dwarf planets Ceres and Pluto, and also on the icy moons of Jupiter, Saturn, and Neptune.

NASA is on the hunt for this water, for the main reason that it’s the key ingredient for the evolution of Earth-type life. Where liquid water exists, if there are organic molecules and energy sources as well then the stage is set for life having evolved independently of Earth. And if we can find that that’s the case somewhere, anywhere else in the Solar System, then that would be a huge – no, make that giant – step toward answering the Big Question: are we alone in the Universe?

Today NASA scientists held a conference about the search for oceans beyond Earth, and how we are currently and plan to find out where and how much is (or even was) out there. An infographic accompanied the press materials released.

“What we’re finding out is that the Solar System really is a soggy place.”

– Dr. Jim Green, NASA’s Planetary Science Director

Check out the full infographic below, along with a video of the conference.

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What Will We Name the Features on Pluto? You Decide.

Artist's impression of Pluto and Charon's surfaces (via SETI and Mark Showalter)

Artist’s impression of Pluto and Charon’s surfaces (via SETI and Mark Showalter)

This July the New Horizons spacecraft will perform its long-awaited flyby through the Pluto system, capturing unprecedented data and images of the distant icy planet and its companion satellites Charon, Nix, Hydra, Kerberos, and Styx. The first two worlds, in particular, will have their surfaces seen in high-resolution, allowing scientists to observe and map their features for the very first time. But as landforms come into view – craters, mountains, scarps, plains, and who knows what else – what will they be named?

This is where YOU come in.

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Eppur Si Muove: Galileo’s Big Night

Note: This is an edited repost of an article from 2014.
Jupiter and the fours "Galilean moons" Europa, Io, Callisto, and Ganymede. (Jan Sandberg/

Jupiter and the four “Galilean moons” Europa, Io, Callisto, and Ganymede. (Jan Sandberg/

405 years ago tonight, January 7, 1610, the Pisan astronomer Galileo Galilei looked up at a bright Jupiter at opposition through his handmade telescope and saw three little “stars” next to it, which piqued his natural scientific curiosity. He soon realized that these little objects weren’t stars at all but rather moons orbiting the giant planet (and, most importantly, not Earth). Further observations over the next few nights showed that the planet wasn’t moving relative to the little “stars” as it should if they were indeed background stars, and in fact the smaller bodies (of which he soon saw four) were moving along with Jupiter each in its own little orbit. This revelation helped change our entire view of the Solar System, causing no end of trouble for Galileo (as the Church didn’t appreciate data contradicting their conveniently Earth-centered Universe) but also opening the door for the discovery of many more moons around other planets.

Today Jupiter is now known to have at least 50 moons, with possibly as many as 67!

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