planets – Australian Science

What do Mars and Australia have in common?

Markus — Tue, 11 Jun 2013 00:29:45 +0000

If you’re expecting a punchline to that title, then guess again. It’s no joke. Surprisingly, Australia shares some remarkably similar geology to our neighbouring planet. Specifically the Red Centre, the arid heart of Australia, is the most Mars-like place on Earth!

It’s possible that people may have mused on the similarities already. After all, with its strikingly rich colours, the Red Centre (more often known as the Outback) certainly looks like few other places on Earth. Without any vegetation, the colour of the soil and rocks in the region could easily resemble Mars in places. But evidently, this resemblance is more than just skin deep. The clue that lead to this fascinating realisation? Another of Australia’s most beautiful and iconic of things – opals.

A view from the top of Uluru, showing it’s distinctive red colour. Credit: Binarysequence/Wikimedia Commons

Patrice Rey at the University of Sydney’s School of Geosciences was investigating how opals formed. It may be surprising to learn that opals are found in few other places on Earth, with roughly 90% of all opals worldwide having originated in Australian mines. Beautiful and sought after, there’s been a lot of mystery behind opals for a long time – specifically about how they form, why they’re found at such shallow depths under the Australian soil, and why they’re found nearly nowhere else on Earth.

The story of these beautiful sparkly gemstones, it turns out, began around 100 million years ago. At the time, most of central Australia was covered by the Eromanga Sea. In times past, this huge epicontinental (inland) sea covered what is now known as the Eromanga Basin – spanning an area of one million square kilometres and reaching into much of what is now Queensland, the Northern territories, South Australia and New South Wales.

During the Cretaceous period, when dinosaurs still ruled our planet, this sea would have been teeming with prehistoric life. But much like the dinosaurs, the Eromanga Sea was doomed. Around 100 million years ago, the climate of Earth began to change and the sea began to dry out. The sea dried out rapidly on geological timescales, to cover a much smaller area. The result was that the chemistry of the surrounding rocks began to change.

As the Eromanga Sea dried out, pyrite minerals in the surrounding rocks began to release sulfuric acid, causing acid weathering on a huge scale – quite possibly the largest Earth has ever seen. The opaline silica which was created in the Australian rocks during this process would later go on to form into opals. But the big clue is the acid weathering – we only know of one other place in the Solar System where this has happened in the past. Planet Mars.

While the predicament of prehistoric Australia is, as far as we know, unique on Earth, Mars actually shares a lot in common with this event. Except on Mars, we believe that the drying out of seas happened on a global scale. Hints of this were detected in 2008, when NASA’s twin Mars rovers, Spirit and Opportunity, detected several telltale clues in the Martian soil.

The surface of Mars was found to hold opaline silica, iron oxides, and certain types of clay. All of these clues led areologists* to conclude that the surface of Mars had been subject to huge amounts of acid weathering. The exact same type of acid weathering which Rey and his fellow researchers have now discovered to have happened in Australia!

An opal doublet from Andamooka, South Australia. Credit: CRPeters/Wikimedia Commons

If you’re thinking that this means that there may be Martian opals waiting to be discovered somewhere on the planet next door, it’s hard to say. But it’s certainly a possibility! There is, however, one final step in the formation of opals. The opaline silica which was found on Mars is not yet true opal. In Australia, the surrounding rock has an impressive capability to neutralise acid. This means that after the ground in Australia became riddled with opaline silica, the surrounding conditions quickly went from acid to alkaline. When this happens before the silica trapped in rock cavities dehydrates and solidifies – voila! Opals! Of course, there’s a good chance that Mars may be home to some kinds of rock which can also neutralise acid the same way.

So only time will tell. Perhaps someday in the future, Martian colonists may be using Mars opals to create the first ever jewellery made elsewhere in the Solar System!

*An areologist studies the geology of Mars, seeing as technically the “geo” in geology refers to planet Earth.

Could there be opals hiding under the Martian soil? Credit: NASA/JPL

Cite this article:
Hammonds M (2013-06-11 00:29:45). What do Mars and Australia have in common?. Australian Science. Retrieved: Apr 28, 2024, from http://australianscience.com.au/geology/what-do-mars-and-australia-have-in-common/

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The post What do Mars and Australia have in common? appeared first on Australian Science.

It’s a small world after all

Markus — Mon, 11 Mar 2013 00:20:42 +0000

What we know of exoplanets has developed at the same time as the technology which we use to discover them. This is, in my opinion, the most exciting thing about the entire field of study. For instance, when we first started spotting planets around alien suns, we found huge gas giants. Hot jupiters, extremely massive and close to their parent stars. For a while, some conjectured that this type of planet may be quite common in the Universe. But since then, we’ve developed more powerful methods of searching the sky and, as it turns out, smaller planets are much more common than huge superjovian worlds. The latest piece in the puzzle comes courtesy of NASA’s Kepler space teescope. Near the end of last month, NASA announced the discovery of the smallest exoplanet ever found around a sun-like star!

Kepler-37b really is tiny. In fact, the whole Kepler-37 system is tiny – the entire system discovered so far can fit inside the orbit of Mercury! The innermost little world is under 100th the mass of Earth, it’s expected to have a radius of around 3867 km (assuming the same average density as the planets in our own solar system) making it smaller than Earth’s moon. One can only apprehensively wonder if this will spark yet another debate over how large an object has to be before it’s considered a planet. With such a tiny orbit, it also has a year lasting just 13 Earth days. Even though the star Kepler-37 is slightly smaller and cooler than the Sun, it’s still enough to heat the surface of tiny 37b to a roasting 700 Kelvin (nearly 430°C). Needless to say, while we all like stories which talk about potential alien life, this is unlikely to be a home for any lifeforms we might recognise.

Kepler-37b is very definitely the runt of the litter. Its sibling worlds, denoted by the letters c and d, are respectively slightly smaller than Earth and about twice the size of Earth. Of course, these planets are also very close to their parent star. The interesting thing is that we’re discovering more and more small worlds around other stars. More and more exoplanet astronomers are warming to the idea that small rocky planets are likely to be the most common in our galaxy. Our current technology might have trouble spotting them further than a certain distance from their parent stars, but they’re likely to be out there waiting to be found.

Even detecting Kepler-37b was quite a notable feat. It was only possible, in fact, because of a set of rather special circumstances. The star Kepler-37 is particularly quiet, lacking the noisy sunspots and features which cause brightness variation in most stars, making it a particularly clear target. It’s also relatively bright in Kepler’s field of view.

To learn more about this star, and hence get greater accuracy on the measurement of the planets it carries in tow, NASA astronomers used a technique known as asteroseismology. Not dissimilar to the way geologists measure earthquakes, asteroseismology is the study of vibrations within a star, measured by accurately observing pulsations in the star’s surface. All stars are constantly bubbling and boiling, and this causes the whole star to vibrate at a number of resonant frequencies – soundwaves – in exactly the same way a bell vibrates when it rings. By measuring the precise frequencies of those soundwaves, a lot can be determined about the interior of a star. Incidentally, this same technique can be used to effectively “listen” to the Sun.

Interestingly, because Kepler-37 has such an eerily peaceful surface for a star, it was very easy to measure those vibrations, making Kepler-37 the smallest star ever to be studied this way. Normally, only large stars are observed using asteroseismology because the measurements need to be very precise. Conveniently though, the Kepler telescope was built for breathtaking precision.

A tiny planet discovered orbiting a singing star 215 light years away. How poetic!

Image credits:
Top – NASA/Ames/JPL-Caltech
Middle – Karl Tate/ © space.com
Bottom – NASA/Ames/JPL-Caltech

Cite this article:
Hammonds M (2013-03-11 00:20:42). It's a small world after all. Australian Science. Retrieved: Apr 28, 2024, from http://australianscience.com.au/space/its-a-small-world-after-all/

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The Case for Neptune

Sharon — Mon, 03 Dec 2012 07:30:07 +0000

Take a moment to consider Neptune. The eighth planet in our solar system, the planet farthest from the Sun, and the third most massive planet in our solar system. Also one of the least visited, and consequently one of the least understood planets in our solar system. Neptune was discovered in 1846. Forty years later, in 1886, astronomer Sir Robert Ball wrote ‘Besides this brief sketch of the discovery of Neptune, we have little to tell with regard to this distant planet. With a good telescope and a suitable magnifying power we can indeed see that Neptune has a disc, but no features on that disc can be identified’.

Unfortunately in the last 126 years not much has changed. Due to its enormous distance from Earth (~ 30 Astronomical Units) Neptune remains little more than a blurry disk in the eyepiece of the most powerful ground based telescopes. In the past astronomers studied Neptune by examining the planet as it occulted, or passed in front of the light of another object, usually a star, allowing scientists to calculate its diameter, chemical composition, and temperature. The opportunity to study the gas giant only improved when Voyager flew by Neptune in 1989, and the Hubble Space Telescope was launched in 1990.

Voyager 2 launched in 1977, and reached Neptune on the 25th of August 1989 (click here for an impressive animation of the Voyager 2 flyby of Neptune). Although Voyager 2 began imaging the planet from about 35,000,000 million miles out, most of the data we have today is from a 24 hour period, during which Voyager 2 passed 4,500 kilometres above Neptune’s north pole at an eye watering 67,000 km per hour. During the trip to Neptune Voyager gathered about 5 trillion bits of information or about .5 of a Terabyte of data. That doesn’t sound much now, but back in 1977 the 3 computers on the Voyager spacecraft had a combined memory of 68Kb, so Voyager sent back almost 15 million times more data that could be stored in it’s memory!!

Scientists were thrilled by the data from Voyager 2 and set to work learning as much as they could about the distant blue planet. We learnt that Neptune is mostly composed of gas, is likely to have a rocky or metallic core, and that the majority of Netpune’s mass is hydrogen and helium, with traces of water, methane, ammonia, and other compounds. Thanks to Voyager 2 we learnt an enormous amount about Neptune’s atmosphere, weather systems, magnetic field, moons, and ring system. But that was over 30 years ago – and we now have more questions than answers.

Images from Voyager 2 showed that the most obvious feature of Neptune is its stunning blue colour, the result of methane in the atmosphere. Voyager 2 also revealed a more dynamic and turbulent atmosphere than anyone expected. Neptune’s atmosphere consists of layers of clouds, banded features, and unexpected structures, including what was termed the Great Dark Spot (GDS). Neptune generates the strongest jet streams anywhere in the solar system, reaching speeds of up to 2,400 kms per hour. Voyager detected weak auroras, similar to those on Earth, but because of Neptune’s complex magnetic field, the auroras appear over wide regions of the planet, not just near the planet’s poles. Despite what we do know, the structure and composition of Neptune’s atmosphere remains poorly understood. What accounts for the relatively high percentage of methane and lack of hydrogen and helium? What is the energy source responsible for powering the incredibly high speed winds and variable storm systems? What happened to the Great Dark Spot (observed by Voyager in 1989, but no where to be seen when Hubble observed the planet in 1994). Why is the temperature of Neptune’s thermosphere, a staggeringly high 750K (4760 degrees celsius)? How can Neptune be so cold and distant from the Sun, and yet radiate so much energy?

Thanks to Voyager 2 we know that Neptune’s magnetic field is approximately 25 times stronger than Earths, and that it’s lopsided (like Uranus), at 47^oto the rotation axis and offset from the planet’s centre. Although we suspect that Neptune’s magnetic field is generated by currents within Neptune’s icy mantle – we do not fully understand why Neptune’s magnetic field is oriented the way it is, or what processes could generate such an off-kilter magnetic field.

Voyager 2 image of Triton (Credit NASA)

Before Voyager 2, Neptune was thought to have 2 moons, Triton and Nereid. Voyager 2 discovered 6 new moons, and since Voyager’s visit, astronomers have discovered a further 5 moons. Most of what we know of Triton, Neptune’s largest satellite, was acquired in a single encounter by the Voyager 2 spacecraft, which imaged about 40% of its surface. If scientists were surprised by the images from Neptune, they were stunned by the images of Triton. Triton, is an icy moon with a surface temperature of -235^o, the coldest place known in the solar system. Voyager’s images revealed a geologically active planet, geysers spewing nitrogen gas and dust particles high into the atmosphere, rocky outcrops, canyons, and plains of frozen methane. Triton has a very thin nitrogen atmosphere with small amounts of methane, above a scarred and cracked surface. Triton showed no fresh impact craters, an indication of an active planet experiencing periodic resurfacing. But there’s still a lot to learn. Perhaps the most tantalising questions are about Neptune’s largest moon. Was Triton formed near Neptune, or is it a captured object from the Kuiper belt? What is the composition of Triton, and what causes the geologic activity, and has the distribution of the ice geysers changed dramatically since the Voyager flyby? Will further analysis of Triton tell us more about the solar system, and our place in it? Is there a sub surface ocean? Could Triton harbour life?

Earth-based observations during the 1980s suggested that there were a number of partial rings surrounding Neptune, and Voyager 2 discovered a system of equatorial, circular rings. Although Voyager 2 gave us a good look at Neptune’s rings, the details of their composition is still uncertain, we don’t know how long they’ve been there, or even if they are stable.

Despite the valuable insights bought to us by the Voyager mission, the Hubble Space Telescope and other studies, clearly there are still a number of questions about Neptune that still need to be answered. Technology has advanced enormously since 1977 and any new mission would be well equipped to examine Neptune, its rings and a number of its moons. A mission to Neptune would enable us to learn more about our outer solar system, and exploration of Triton may provide our best opportunity to examine the surface and atmosphere of a Kuiper Belt Object in orbit around a planet in our solar system. In 2003 NASA proposed a Neptune Orbiter/Triton Explorer, however, that mission appears defunct. Neither NASA nor ESA have any current or future plans for the exploration of Neptune.

I think that needs to change.

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