Planet

The first Cassini to explore Saturn was a person

Saturn
TWO CASSINIS The Cassini spacecraft has become famous for its stunning views of Saturn, including this image of the unlit side of the rings taken in 2012. But what do we know about the man Cassini was named for?

As the Cassini spacecraft plunges toward its death on Saturn, the world’s knowledge of the famous ringed planet continues to accumulate. Thanks to years of observations by the versatile probe, astronomers now know Saturn as intimately as macaroni knows cheese. But still hardly anyone outside the world of astronomy knows anything about Cassini — and I don’t mean the spacecraft, but the guy it was named for.

Gian Domenico Cassini was an Italian astronomer, born in Perinaldo in 1625, around the time that Galileo was battling the church over Copernicus’ revelation that the Earth orbits the sun. Cassini was attracted to poetry but was also good at math. He got his start in science via astrology, which back then was not considered quite as completely idiotic as it is today. In fact, astronomy itself was often supported by wealthy people in order to get better astrological forecasts. One such wealthy Italian, an amateur astronomer, was impressed with a pamphlet on astrology that Cassini had written; it earned him an invitation to work at the amateur’s observatory, near Bologna.

From the leading scientists at Bologna, Cassini learned the importance of using high-quality instruments to make the most precise measurements possible. His talents were soon recognized; by 1650 Cassini’s accomplishments and reputation earned him the chair in astronomy at the university in Bologna. He continued his research during the 1650s, taking a particular interest in comets.

Gian Domenico Cassini was an Italian astronomer who studied comets, the sun and solar eclipses. After mastering the moons of Jupiter, he turned to Saturn.

Cassini was an old-school conservative kind of scientist, not even inclined to take Galileo’s side on the Earth-orbiting-the-sun issue. Cassini preferred Tycho Brahe’s position that the other planets orbited the sun, but the sun then orbited the Earth. (Later Cassini accepted the Copernican sun-centered solar system, but only half-heartedly.) Cassini also was no fan of Newton’s law of gravity.

Cassini’s work as an eminent Italian scientist was not limited to astronomy. Called on to referee a…

Watery exoplanet’s skies suggest unexpected origin story

HAT-P-26b illsutration
WET AND WILD The exoplanet HAT-P-26b, illustrated here, has relatively low levels of heavy elements in its atmosphere, compared with those found in Neptune’s atmosphere. As a result, the exoplanet may have had a different origin story than ice giants in our solar system.

A watery world about 430 light-years from Earth may have had a relatively calm origin.

The Neptune-mass exoplanet, HAT-P-26b, has surprisingly low levels of heavy elements in its atmosphere, suggesting that it formed close to its star, researchers report in the May 12 Science. That’s different from how the ice giants in Earth’s solar system, Neptune and Uranus, formed, suggesting possible new insights into different ways planetary systems originate throughout the galaxy.

“With the observations of exoplanets’ atmospheres, we are looking outward to look in,” says study coauthor Hannah Wakeford, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md.

Scientists mostly use computer simulations to try to understand how planetary systems form. These simulations are based, in part, on how the planets in Earth’s solar system coalesced, but it’s unclear how common these types of planetary origins are. Many Neptune-sized worlds, for instance, have orbits vastly different than the ice giants of Earth’s system. But if the abundances of heavy elements in atmospheres of exoplanets in other systems resemble the abundances for planets of similar mass…

Japanese Space Agency’s Mission Aims To Uncover How Moons Of Mars Formed

NASA/JPL/Handout via Reuters

The Japan Aerospace Exploration Agency (JAXA) has announced a mission to visit the two moons of Mars and return a rock sample to Earth. It’s a plan to uncover both the mystery of the moons’ creation and, perhaps, how life began in our Solar System.

The Solar System’s planets take their names from ancient Greek and Roman mythology. Mars is the god of war, while the red planet’s two moons are named for the deity’s twin sons: Deimos (meaning panic) and Phobos (fear).

Unlike our own Moon, Phobos and Deimos are tiny. Phobos has an average diameter of 22.2km, while Deimos measures an even smaller 13km. Neither moon is on a stable orbit, with Deimos slowly moving away from Mars while Phobos will hit the Martian surface in around 20 million years.

The small size of the two satellites makes their gravity too weak to pull the moons in spheres. Instead, the pair have the irregular, lumpy structure of asteroids. This has led to a major question about their formation: were these moons formed from Mars or are they actually captured asteroids?

Our own Moon is thought to have formed when a Mars-sized object hit the early Earth. Material from the collision was flung into the Earth’s orbit to coalesce into our Moon.

A similar event could have produced Phobos and Deimos. The terrestrial planets were subjected to a rain of impacts during the final throes of Solar System formation.

Mars shows possible evidence of one such major impact, as the planet’s northern hemisphere is sunk an average of 5.5km lower than the southern terrain. Debris from this or other impacts could have given birth to the moons.

Alternatively, Phobos and Deimos could be asteroids that were scattered inwards from the asteroid belt by the looming gravitational influence of Jupiter. Snagged by Mars’s gravity, the planet could have stolen its two moons. This mechanism is how Neptune acquired its moon, Triton, which is thought to have once been a Kuiper belt object, like Pluto.

There are compelling arguments for both the #TeamImpact and #TeamCapture scenario.

The orbits of the two moons are circular and in the plane of Mars’s own rotation. While the chance of this happening during a capture event are extremely low, observations of the moons suggest they may have a composition similar to that of other asteroids.

Definite determination of the moons’ composition would act as a fingerprint to distinguish the two models. A collision event…

New Super-Earth May Be Best Yet for Finding Signs of Life

It was only a couple of weeks ago that astronomy fans were all excited about planet GJ 1132b, which shows evidence of an atmosphere. But the information from outside our solar system comes thick and fast (scientists have catalogued over 3,400 exoplanets), and now we have planet LHS 1140b to get excited about. Why? This planet, 40 light years away in the constellation Cetus, might have the conditions necessary for life. Specifically, it is a rocky planet with an orbit around its sun that…

NASA Puts the Planet Up for Adoption in Time for Earth Day

If you’re looking to feel a deeper connection to the planet you call home, NASA has good news. As Smithsonian.com reports, the space agency is putting Earth up for adoption one 55-mile-wide section at a time.

The project launched on April 6 in anticipation of Earth Day on April 22. Unlike other programs that invite you to symbolically adopt a panda or a star, this process doesn’t require a donation. Just type in your name and NASA will assign you one of 64,000 adoptable locations that cover the globe. The areas are divided into hexagonal tiles, each accompanied by Earth…

Keep the Whole Solar System to Yourself in This Tiny Bottle

Ever dream of carrying the entire universe around in your pocket? Now you can with a little help from the 3D printing company Little Planet Factory. The online store creates and sells itty-bitty planets that you can hold in your hand. Their most adorable product might be a small bottle that contains all the planets of the solar system—which are at a scale of 1:5,000,000,000. That means Jupiter is the size of your fingernail,…

It’s time to redefine what qualifies as a planet

Pluto
PLANET OR NOT? A group of planetary scientists label Pluto and many other orbs in the solar system as planets, despite the definition set down by the International Astronomical Union in 2006.

Pluto is a planet. It always has been, and it always will be, says Will Grundy of Lowell Observatory in Flagstaff, Arizona. Now he just has to convince the world of that.

For centuries, the word planet meant “wanderer” and included the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. Eventually the moon and sun were dropped from the definition, but Pluto was included, after its discovery in 1930. That idea of a planet as a rocky or gaseous body that orbited the sun stuck, all the way up until 2006.

Then, the International Astronomical Union narrowed the definition, describing a planet as any round object that orbits the sun and has moved any pesky neighbors out of its way, either by consuming them or flinging them off into space. Pluto failed to meet the last criterion (SN: 9/2/06, p. 149), so it was demoted to a dwarf planet.

Almost overnight, the solar system was down to eight planets. “The public took notice,” Grundy says. It latched onto the IAU’s definition — perhaps a bit prematurely. The definition has flaws, he and other planetary scientists argue. First, it discounts the thousands of…