Today’s news is dominated by all things planetary, and features stories about exploding dunes on Mars, exploding meteors at Jupiter, and the dirty gritty stuff that isn’t coating Saturn’s ring materials. We also add a side dose of neutron star to round things out.
Mars Terrain Maps
The Age of Saturn’s Rings
Max Massed Neutron Star Identified
Today’s news starts with a look at the explosive busting out of spring on Mars. Like Earth, the red planet is tilted, and this causes seasonal variations in the temperatures and weather. Winter on Mars doesn’t mess around – it gets so cold that gases like carbon dioxide freeze out of the atmosphere, creating layers of ice on the surface. Carbon dioxide ice here on Earth and on Mars acts much the same way: it goes straight from a solid frozen state to a gaseous state that takes up a whole lot more space than the ice. It’s the great expansion that makes spring on Mars something special. As temperatures warm with the oncoming summer, the frozen ice violently goes from ice to gas, exploding outwards and revealing dark sand from beneath the surface. In a new image from the ExoMars mission, we see vast fields of sand dunes rising up from the Martian plains, and these Dunes are outlined in dark splotches all along their bases. These weird ink splotch looking markings are places where sublimating ice has exploded outward. So, um, future Martian explorers, I’d like to recommend you don’t try going on a pleasant walk through the dunes in the spring; you just might find the ground beneath your feet exploding.
It’s likely Mars will be in the news more and more in the coming months as planetary scientists frantically do as much preparatory science as they can in the lead up the launches of NASA Mars 2020 Rover, and the joint ESA / Rosocosmos Rosalind Franklin Rover. These two complementary missions are hoping to look for evidence of past – and possibly current – life on Mars.
Some of that research is getting released this week at the European Planetary Science Congress, which is currently being held in Geneva, Switzerland. In one study released yesterday, planetary scientists are releasing Digital Terrain Models that allow virtual exploration of the sites soon to be explored in reality. One of the sites being explored is Oxia Planum, the selected landing site for the Franklin Rover. This is a fairly flat area that was once a river bed. This ancient terrain is a site of clay minerals and might still have traces of life. These kinds of detail maps combine light and dark shading to highlight slopes with colors that indicate altitude. These maps make even the smallest ripples in sand dunes visible in maps that have 25cm resolutions. These images can now be used to plan how the rover will move through this plain and where it will go searching for traces of life. To create these maps, planetary scientists combined images that were taken at slightly different angles with other digital data, all of which exists in publicly accessible archives. This means, if you need a new 3D reality for your digital projects, Mars data is ready and waiting for you to explore.
From cool new maps of Mars, we move out to accidental discoveries on Jupiter. Back in August, amateur astronomy Ethan Chappel of Cibolo, Texas recorded a bright flash on Jupiter while he was making a video of Jupiter. Because this was video, with each frame stored separately, this data made it possible for researchers to study the how the flash grew and faded away. This work, done by the Florida Institute of Technology researchers Ramanakumar Sankar and Csaba Palatai, was able to determine the overall energy output and the kind of object required. In this case, they find a 12-16m diameter rock with a mass of 450 tones likely disintegrated 80km above Jupiter’s clouds. This mass – size combination is consistent with a stony-iron meteor impacting Jupiter.
This kind of detection is becoming more and more common. This isn’t because Jupiter is getting impact more frequently, but rather what we’re seeing is a growing number of amateur astronomers purchasing and using highly-sensitive digital detectors and pointing them at Jupiter. In the past 10 years, 6 different flashes have been observed, and this was the second brightest. It is now estimated that 20-60 impacts like this occur each year. This is one of my favorite cases of models being forced to change as we gather new data. Back in 1994, when the comet Shoemaker Levy 9 hit the surface of Jupiter, it was frequently claimed this was a once in a lifetime event, and that impacts of Jupiter might only occur every few decades to every few centuries. Nope – we were wrong. While it may have been a once in a lifetime event to see a shattered comet hit Jupiter, it turns out that collisions in general are extremely common, and any of us – well, any of us with a telescope and digital detector – have the potential to capture this kind of an event.
As we continue our journey out of the solar system, our next story takes us from Jupiter outwards toward Saturn and its ring system. These rings are one of the most beautiful and confusing objects in the Solar System. How did they form? There is no consensus. How long will they last? Good question. How old are they? Well.. there is a lot of debate.
Basically, the rings are a pretty enigma that refuse to give away their secrets.
In a new paper published in Nature Astronomy and presented at EPSC in Geneva, scientists from the French Observatoire de la Cote d’Azur put forward a new way of looking at the rings’ age. It had previously been suggested that the bright, clean surface of the ice in the rings means the rings are young, maybe only a few tens of millions of years old. Put differently, when Cassini plunged through the rings in 2017, the ring material appeared to be clean and bright like newly fallen snow, and wasn’t gross and covered in dust and organic materials like city snow that has been around for a few weeks. While buses and cars aren’t out polluting the rings’ materials, our solar system does a good job messing up fresh ice by bombarding it with micrometeorites and dust. When we see dirty surfaces, we assume they are old, and when we see shiny bright surfaces we assume they are young, and we guess how old or young things are in general by their degree of, well, grossness.
In this new paper, however, researchers led by Aurelian Crida suggest that while there are plenty of organic materials and silicate grains in the Saturnian system, these pollutants are being dynamically cast out through processes that drive these materials to fall into Saturn’s atmosphere or to be flung outward out of the rings. This is consistent with Cassini’s Cosmic Dust Analyzer finding 600 kilograms of silicate grains fall on Saturn from the rings every second, and also with measurements from a different Cassini instrument that found organic molecules are also falling from the rings into the atmosphere.
So this raises the question, if Saturn’s rings are essentially self cleaning and we can’t use the buildup of pollutants to get at age, how can we get at the rings’ age? Well, one of the old stand-bys is looking at the spread of the material. It’s expected that young rings would still have the material clumped up, and it’s only over time that the ring material will spread out into the distribution we see today. This kind of a classic dynamical argument gets us an age of about 4 billion years, or an age that matches the age of many other objects in our solar system. While it’s possible for rings to relax out faster, or to form with more spread out material, this would require special coincidences to take place, and this team posits that sometimes the simple answer is the best answer, and forming the rings early in the universe and having their dynamical age match their actual age and match the age things normally formed in our Solar System. Well… it just makes sense.
While this week is a week filled with Planetary Science, that doesn’t mean no other science is going on. For our last story of the day, we look at two small objects with great masses.
In particular, we are looking at neutron star J0740+6620, a massive stellar remnant that co-exists with a white dwarf companion. White Dwarf stars are the cores of stars like our Sun that remain after a dying star exhales its atmosphere into a Planetary Nebula. These objects are under 1.44 solar masses, and are roughly the size of Earth’s moon. The reason they can’t get larger than 1.44 solar masses is a problem of particle physics. White dwarfs are supported by what is called electron degeneracy pressure. The electrons are all pushing on one another, and are limited in what configurations they can have by the Pauli Exclusion Principal. This electron on electron pressure pushes outward against gravity, which is trying to crush those electrons and all the other particles together. At a certain point, however, the electron degeneracy pressure just can’t support the star anymore. When this pressure is exceeded while a massive star is dying, you can end up with the remnant instead collapsing down, combining electrons and protons to form neutrons, and creating what we call a neutron star – a star supported by neutron degeneracy pressure.
These heavy mass objects are only about the size of Manhattan Island, and also have a maximum mass – in this case somewhere around 2.16 solar masses. I say somewhere around because the exact limit has to factor together not just the mass of the star, but also its rotation rate and other factors. Above this mass, neutron stars can no longer support themselves and they will collapse under gravity into a black hole.
All this background is necessary to understand why J0740+6620 is so interesting. By looking at how this neutron star orbits with its white dwarf partner, it becomes possible to measure its mass very accurately, and this mass is 2.17 solar masses, right on the boundary of what is allowed. This boundary is reinforced by LIGO results that have documented the self destruction of neutron stars during merger events. Finding this kind of an object on the edge of what is allowed is exciting, and this paper also just has data that is cool to look at. One of the unique characteristics of neutron stars is they can release pulses of radio emission as they rotate extremely rapidly. Called pulsars, these special neutron stars are more accurate in their timing than any human made clock. When these objects are in binary systems, or when they have planets, we see pulsar timing variations. As the pulsar moves away from us, its pulses get spread out, as each has to travel a bit to reach us. When the pulsar moves toward us, its pulses get pushed together as each has to travel a smaller distance. In this neutron star and white dwarf binary system we can actually hear the orbits of the stars … or we can them if we exaggerate the millionth of a second change in this millisecond pulsars pulses. This kind of science is just fun, and who doesn’t love to find the biggest known of a cool kind of object … especially when that object is only 30km across and 4600 light years away.