ESA’s Mars Express has captured an unusual and rare occultation, all from its vantage point in orbit of Mars. The spacecraft’s orbit brought it to the right place where it could witness the moment Mars’ small moon Deimos passed in front of Jupiter and its four largest moons. Scientists say that celestial alignments like these enable a more precise determination of the Martian moons’ orbits.
How great are wheels, really? Wheels need axles. Suspension. Power of some kind. And roads, or at least swaths of relatively flat and stable terrain. Then you need to maintain all of it. Because of their cost many civilizations across human history, who knew all about wheels and axles, didn’t bother using them for transportation. Another way to look at it – much of human technology mimics nature. Of the simple machines, levers, inclined planes, wedges, and even screws are observed in nature. Why not the wheel?
The origin of Phobos and Deimos, the two Martian moons, has been a mystery to astronomers. These two bodies are a fraction of the size and mass of the Moon, measuring just 22.7 km (14 mi) and 12.6 km (7.83 mi) in diameter. Both have a rapid orbital period, taking just 7 hours, 39 minutes, and 12 seconds (Phobos) and 30 hours, 18 minutes, and 43 seconds (Deimos) to complete an orbit around Mars. Both are also irregular in shape, leading many to speculate that they were once asteroids that got kicked out of the Main Belt and were captured by Mars’ gravity.
There’s also the theory that Phobos and Deimos were once a single moon hit by a massive object, causing it to split up (aka. the “splitting hypothesis”). In a recent paper, an international team of scientists led by the Institute of Space and Astronautical Science (ISAS) revisited this hypothesis. They determined that a single moon in a synchronous orbit would not have produced two satellites as we see there today. Instead, they argue, the two moons would have collided before long, producing a debris ring that would have created an entirely new moon system.
In a recent study published in Earth and Planetary Astrophysics, a team of researchers from the University of Texas at Arlington, Valdosta State University, Georgia Institute of Technology, and the National Radio Astronomy Observatory estimated how many moons could theoretically orbit the Earth while maintaining present conditions such as orbital stability. This study opens the potential for better understanding planetary formation processes which could also be applied to identifying exomoons possibly orbiting Earth-like exoplanets, as well.
Our Solar System contains eight planets and more than 200 moons. The large majority of those moons have no chance of being habitable, but some of them—Europa and Enceladus, for example—are strong candidates in the search for life.
The Moon has orbited Earth since the Solar System’s early days. Anyone who’s ever spent time at the ocean can’t fail to notice the Moon’s effect. The Moon drives the tides even in the world’s most remote inlets and bays. And tides may be vital to life’s emergence.
But if Earth were more massive, the Moon may never have become what it is now. Instead, it would be much smaller. Tides would be much weaker, and life may not have emerged the way it did.
Data from the Cassini mission keeps fuelling discoveries. The latest discovery is that Saturn’s tiny moon Mimas may have an internal ocean. If it does, the moon joins a growing list of natural satellites in our Solar System that may harbour liquid water under their surfaces.