Head in the clouds of astrophysics... again

Behold, it's that time of year again where the holidays are starting, families are back together and the out of office emails are switched on. Having completed my first term at Cambridge, possibly the most compact 8 weeks of my life, and now that I've had a week to recover from the crescendo of activity that reaches its peak at the end of term, I'm back on the blog to muse about astrophysics.

I set my laptop wallpapers to rotate every minute through an album of my favourite 100 (mainly astronomical) images, which keeps me on my toes as I try to remember the names of an ever expanding catalogue of stars, planets, galaxies, moons and now also Cambridge colleges. This prompted me to make use of my holiday time to ponder the universe once more, and the plethora of stuff that drifts through the interstellar medium.

In no particular order, here are some of the exciting things I have covered this term (as well as a random pretty stars photo, to remind us of the bigger picture and systems around which planets evolve).

Hot Springs on Earth

Grand Prismatic Spring, Yellowstone National Park USA. Credit: Paul Riffer photography.

This term I have been studying the origins of planets and habitable environments. For the first time I've studied some geology and mineralogy, and even revisited chemistry which I haven't seen much of since school. Next term I shall plunge into biology, with the origin and detection of life and biosphere modules. It has been enjoyable learning about new science from scratch and building on my back catalogue of astrophysical knowledge I have accumulated over the years of reading NASA blog posts.

NASA is well known for its stunning images of the moon, planets, stars and galaxies, but less well known is the work it does on Earth. This incredible landscape is not from an alien planet but our own, located in Yellowstone National Park in the USA. This national park contains the most concentrated array of hot spring and geysers in the world, and this stunning shot shows the largest, the Grand Prismatic Spring, which meaures 90m in diameter and 50m deep. Being a swimmer, my first question to the lecturer was whether one could splash around in it. Sadly the answe was no, as it is extremely acidic and therefore lethal, so must be admired from a distance. It is also 87 degrees Celsius in the centre, which makes it too hot to support life. Its edges however are cooler, and habitable to algae and thermophilic (heat-loving) cyano-bacteria, which are responsible for the yellow and orange pigments that act as the bacteria's natural suncream. While it is undeniably pretty, NASA's main interest in exploring this hot spring is because it may share similarities to the environments where life first evolved on Earth. Furthermore, other solar system bodies such as Jupiter's moon Europa may also contain springs or underwater vents hosting geothermal activity, so there is much that can be learnt from studying our own planet which may help when exploring further afield.

Dunes on Mars

Noachis Terra region of dunes, Mars. For scale, it shows an area about 1km across. Image credit: NASA/JPL

Mars is up there as one of the most well known solar system bodies, probably due to it being the most feasible planet for humans to visit one day, since the others are too far away to be practical or have hostile environments. While I generally prefer sharing science that is less well known, there are many beautiful images of Mars and given the interesting lectures we had on it this term, it simply had to be included in this post.

This enhanced-colour image from NASA Mars Reconnaissance Orbiter shows sand dunes trapped in an impact crater in Noachis Terra, Mars. The wind-beaten dunes look similar to ones we might find in Earth's deserts. The pattern and shape of the dunes are affected by changes in the wind's direction and strength, providing a historical record of Martian weather. Mars has some pretty cool features, including ancient river valley networks, deltas and lake beds, and minerals which could only have formed in liquid water, which is thought to have flooded the planet 3.5 billion years ago. Its thin atmosphere means liquid water doesn't stay on the surface for long before evaporating. Nowadays water on Mars can be found in the form of ice under the surface of its polar regions, and as salty water which seasonally flows down some of its hills. The planet is also home to the largest volcano in the solar system, Olympus Mons, triple the height of Earth's Mount Everest. More pretty pictures of Mars can be found here.

Plumes on Saturn's moon

Plumes from Enceladus. Credit: NASA/JPL/SSI; Mosaic: Emily Lakdawalla

For part of my planetary science degree, this term I completed a group project funding pitch arguing the case for sending a mission to Saturn's moon Enceladus. It is thought to contain a rocky core, a subsurface ocean and icy crust. The crust has a few cracks along its southern polar region, through which plumes of droplets and ice grains from the ocean below can escape as geysers. This gives scientists a unique opportunity to explore the otherwise inaccessible material of the moon's interior, and the Cassini mission has already found rich molecules and the elements of Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus and Sulphur in various forms. In planetary science these are known as CHNOPS, and are exciting as they are thought to be key life sustaining molecules. This moon is the only place (other than Earth) in the solar system where all six elements have been found. At the rock-ocean boundary, there may be hydrothermal vents, similar to those at the depths of the Atlantic ridge, where microorganisms able to live without sunlight have been found. Tantalisingly, there is a possibility that similar life may exist on Enceladus too; modelling by this paper suggests that some of the methane detected in the plumes of Enceladus could, in principle, be produced by microorganisms called methanogens. Two missions have been launched to investigate Jupiter's icy moons since 2023, NASA's Clipper mission and ESA's JUICE, and it is clear icy moons will remain a key frontier for space science in the next few years.

Clouds of stars

Large Magellanic Cloud, satellite galaxy of the Milky Way and stellar nursery.

Credit: ESA/Hubble & NASA

In the words of the British band Coldplay, 'a sky full of stars... such a heavenly view'. Astronomy, romance and poetry have long been linked together, and when staring at exquisite images like this it isn't hard to see why. One of my favourite areas of astronomy is star formation, which occurs in dust filled regions such as the Large Magellanic Cloud. This stellar nursery is home to many hot young stars, whose intense ultraviolet light radiation illuminates the surrounding hydrogen gas, while torrential stellar winds carve out surrounding material.

This nearby galaxy is about 1/100th the mass of our Milky Way, and on course for a merger in around 2.4 billion years. It hasn't always been a local neighbour though, and is thought to have formed from a different reservoir of gas to the one that made the Milky Way. The stars within the cloud have preserved the environmental conditions they formed in. The LMC has some relatively metal poor stars, meaning few elements other than hydrogen are abundant. The very first generation of stars in the universe would have formed in a metal free environment of hydrogen with a smattering of helium, and evolved differently to later generation stars which grew from gas enriched with heavier elements, the remnants of exploded previous stars. In this way, the LMC provides a unique window into the properties of metal poor stars like those in the metal poor early universe.

So there we have it, a dazzling array of astronomical images and some thought provoking science to celebrate the holidays. For the next article, I shall be dusting off my maths and physics textbooks to walk readers through a hand picked selection of equations I found on my tablet's wallpaper.