To be sure, Australia is large enough to usually leave some part of our country waiting for rain. So what exactly is a drought, and how do we know when we are in it?
This question matters, because declaring drought has practical implications. For example, it may entitle those affected to government assistance or insurance pay-outs.
But it is also a surprisingly difficult question. Droughts are not like other natural hazards. They are not a single extreme weather event, but the persistent lack of a quite common event: rain. What’s more, it’s not the lack of rain per se that ultimately affects us. The desert is a dry place but it cannot always be called in drought.
Ultimately, what matters are the impacts of drought: the damage to crops, pastures and environment; the uncontrollable fires that can take hold in dried-up forests and grasslands; the lack of water in dams and rivers that stops them from functioning. Each of these impacts is affected by more than just the amount of rain over an arbitrary number of months, and that makes defining drought difficult.
Scientists and governments alike have been looking for ways to measure drought in a way that relates more closely to its impacts. Any farmer or gardener can tell you that you don’t need much rain, but you do need it at the right time. This is where the soil becomes really important, because it is where plants get their water.
Too much rain at once, and most of it is lost to runoff or disappears deep into the soil. That does not mean it is lost. Runoff helps fill our rivers and waterways. Water sinking deep into the soil can still be available to some plants. While our lawn withers, trees carry on as if there is nothing wrong. That’s because their roots dig further, reaching soil moisture that is buried deep.
A good start in defining and measuring drought would be to know how much soil moisture the vegetation can still get out of the soil. That is a very hard thing to do, because each crop, grass and tree has a different root system and grows in a different soil type, and the distribution of moisture below the surface is not easy to predict. Many dryland and irrigation farmers use soil sensors to measure how well their crops are doing, but this does not tell us much about the rest of the landscape, about the flammability of forests, or the condition of pastures.
Soils and satellites
As it turns out, you need to move further away to get closer to this problem – into space, to be precise. In our new research, published in Nature Communications, we show just how much satellite instruments can tell us about drought.
The satellite instruments have prosaic names such as SMOS and GRACE, but the way they measure water is mind-boggling. For example, the SMOS satellite unfurled a huge radio antenna in space to measure very specific radio waves emitted by the ground, and from it scientists can determine how much moisture is available in the topsoil.
Even more amazingly, GRACE (now replaced by GRACE Follow-On) was a pair of laser-guided satellites in a continuous high-speed chase around the Earth. By measuring the distance between each other with barely imaginable accuracy, they could measure miniscule changes in the Earth’s gravitational field caused by local increases or decreases in the amount of water below the surface.
By combining these data with a computer model that simulates the water cycle and plant growth, we created a detailed picture of the distribution of water below the surface.
It is a great example showing that space science is not just about galaxies and astronauts, but offers real insights and solutions by looking down at Earth. It also shows why having a strong Australian Space Agency is so important.
Taking it a step further, we discovered that the satellite measurements even allowed us to predict how much longer the vegetation in a given region could continue growing before the soils run dry. In this way, we can predict drought impacts before they happen, sometimes more than four months in advance.
This offers us a new way to look at drought prediction. Traditionally, we have looked up at the sky to predict droughts, but the weather has a short memory. Thanks to the influence of ocean currents, the Bureau of Meteorology can sometimes give us better-than-evens odds for the months ahead (for example, the next three months are not looking promising), but these predictions are often very uncertain.
Our results show there is at least as much value in knowing how much water is left for plants to use as there is in guessing how much rain is on the way. By combining the two information sources we should be able to improve our predictions still further.
Many practical decisions hinge on an accurate assessment of drought risk. How many firefighters should be on call? Should I sow a crop in this paddock? Should we prepare for water restrictions? Should we budget for drought assistance? In future years, satellites keeping an eye on Earth will help us make these decisions with much more confidence.
December 24 is the 50th anniversary of Earthrise, arguably one of the most profound images in the history of human culture. When astronaut William Anders photographed a fragile blue sphere set in dark space peeking over the Moon, it changed our perception of our place in space and fuelled environmental awareness around the world.
The photo let us see our planet from a great distance for the first time. The living Earth, surrounded by the darkness of space, appears fragile and vulnerable, with finite resources.
Viewing a small blue Earth against the black backdrop of space, with the barren moonscape in the foreground, evokes feelings of vastness: we are a small planet, orbiting an ordinary star, in an unremarkable galaxy among the billions we can observe. The image prompts emotions of insignificance – Earth is only special because it’s the planet we live on.
As astronaut Jim Lovell said during the live broadcast from Apollo 8, “The vast loneliness is awe-inspiring, and it makes you realise just what you have back there on Earth.”
Earthrise is a testament to the extraordinary capacity of human perception. Although, in 1968, the photograph seemed revelatory and unexpected, it belongs to an extraordinary history of representing the Earth from above. Anders may have produced an image that radically shifted our view of ourselves, but we were ready to see it.
A history of flight
People have always dreamed of flying. As we grew from hot-air balloons to space shuttles, the camera has been there for much of the ride.
After WWII, the US military used captured V-2 rockets to launch motion-picture cameras out of the atmosphere, producing the first images of Earth from space.
Russia’s Sputnik spurred the United States to launch a series of satellites — watching the enemy and the weather — and then NASA turned its attention to the Moon, launching a series of exploratory probes. One (Lunar Orbiter I, 1966) turned its camera across a sliver of the Moon’s surface and found the Earth, rising above it.
Despite not being the “first” image of the Earth from our Moon, Earthrise is special. It was directly witnessed by the astronauts as well as being captured by the camera. It elegantly illustrates how human perception is something that is constantly evolving, often hand in hand with technology.
Earthrise showed us that Earth is a connected system, and any changes made to this system potentially affect the whole of the planet. Although the Apollo missions sought to reveal the Moon, they also powerfully revealed the limits of our own planet. The idea of a Spaceship Earth, with its interdependent ecologies and finite resources, became an icon of a growing environmental movement concerned with the ecological impacts of industrialisation and population growth.
From space, we observe the thin shield provided by our atmosphere, allowing life to flourish on the surface of our planet. Lifeforms created Earth’s atmosphere by removing carbon dioxide and generating free oxygen. They created an unusual mix of gases compared to other planets – an atmosphere with a protective ozone layer and a mix of gases that trap heat and moderate extremes of temperature. Over millions of years, this special mix has allowed a huge diversity of life forms to evolve, including (relatively recently on this time scale) Homo sapiens.
The field of meteorology has benefited enormously from the technology foreshadowed by the Earthrise photo. Our knowledge is no longer limited to Earth-based weather-observing stations.
Satellites can now bring us an Earthrise-type image every ten minutes, allowing us to observe extremes such as tropical cyclones as they form over the ocean, potentially affecting life and land. Importantly, we now possess a long enough record of satellite information so that in many instances we can begin to examine long-term changes of such events.
The human population has doubled in the 50 years since the Earthrise image, resulting in habitat destruction, the spread of pest species and wildfires spurred by climate warming. Every year, our actions endanger more species.
Earth’s climate has undergone enormous changes in the five decades since the Earthrise photo was taken. Much of the increase in Australian and global temperatures has happened in the past 50 years. This warming is affecting us now, with an increase in the frequency of extreme events such as heatwaves, and vast changes across the oceans and polar caps.
With further warming projected, it is important that we take this chance to look back at the Earthrise photo of our little planet, so starkly presented against the vastness of space. The perspective that it offers us can help us choose the path for our planet for the next 50 years.
It reminds us of the wonders of the Earth system, its beauty and its fragility. It encourages us to continue to seek understanding of its weather systems, blue ocean and ice caps through scientific endeavour and sustained monitoring.
The beauty of our planet as seen from afar – and up close – can inspire us to make changes to secure the amazing and diverse animals that share our Earth.
Zoos become conservation organisations, holding, breeding and releasing critically endangered animals. Scientists teach us about the capacities of animals and the threats to their survival.
Communities rise to the challenge and people in their thousands take actions to help wildlife, from buying toilet paper made from recycled paper to not releasing balloons outdoors. If we stand together we can secure a future for all nature on this remarkable planet.
The year gets off to a bang with the Quadrantids, the first of the annual big three meteor showers. Active while the Moon is new, it gives northern hemisphere observers a show to enjoy during the cold nights of winter. Sadly, the shower is not visible from southern skies.
The other two members of the big three — the Perseids and Geminids — are not so fortunate this year, with moonlight set to interfere and reduce their spectacle.
So, with that in mind, where and when should you observe to make the best of 2019’s meteoric offerings? Here we present the likely highlights for this year – the showers most likely to put on a good show.
We provide details of the full forecast activity period for each shower, and the forecast time of maximum. We also give sky charts, showing you where best to look, and give the theoretical peak rates that could be seen under ideal observing conditions – a number known as the Zenithal Hourly Rate, or ZHR.
It is important to note that the ZHR is the theoretical maximum number of meteors you would expect to see per hour for a given shower, unless it were to catch us by surprise with an unexpected outburst!
In reality, the rates you observe will be lower than the ZHR – but the clearer and darker your skies, and the higher the shower’s radiant in the sky, the closer you will come to this ideal value.
Despite being one of this year’s three most active annual showers, the Quadrantids are often overlooked and under-observed. This is probably the result of their peak falling during the depths of the northern hemisphere winter, when the weather is often less than ideal for meteor observations.
For most of the fortnight they are active, Quadrantid rates are very low (less than five per hour). The peak itself is very short and sharp, far more so than for the year’s other major showers. As a result, rates exceed a quarter of the maximum ZHR for a period of just eight hours, centred on the peak time.
The Quadrantid radiant lies in the northern constellation Boötes, the Herdsman, and is circumpolar (never sets) for observers poleward of 40 degrees north. As a result, observers in northern Europe and Canada can see Quadrantids at any time of night. The radiant is highest in the sky (and the rates are best) in the hours after midnight.
For this reason, this year’s peak (at 2:20am UT) is best suited for observers in northern Europe – and given that peak rates can exceed 100 per hour, it is certainly worth setting the alarm for, to get up in the cold early hours, and watch the spectacle unfold.
Alpha Centaurids [S]
Active: January 31 – February 20
Maximum: February 8, 1:00pm UT = February 8, 9pm (WA) = February 8, 11pm (QLD) = February 9, 12am (NSW/ACT/Vic/Tas)
ZHR: Variable; typically 6, but can exceed 25
The Alpha Centaurids are a minor meteor shower, producing typical rates of just a few meteors per hour. But they are famed as a source of spectacular fireballs for southern hemisphere observers and so are worth keeping an eye out for in southern summer skies.
Alpha Centaurids are fast meteors, and are often bright. As with most showers that are only visible from the southern hemisphere, they remain poorly studied. Though typically yielding low rates, several outbursts have occurred where rates reached or exceeded 25 per hour.
The shower’s radiant lies close to the bright star Alpha Centauri – the closest naked-eye star to the Solar System and the third brightest star in the night sky.
Alpha Centauri is just 30 degrees from the south celestial pole. As a result, the radiant essentially never sets for observers across Australia. The best rates will be seen from late evening onward, as the radiant rises higher into the southern sky.
This year, the peak of the Alpha Centaurids coincides with the New Moon, making it an ideal time to check out this minor but fascinating shower.
Eta Aquariids [S preferred]
Active: April 19 – May 28
Maximum: May 6, 2pm UT = May 6, 10pm (WA) = May 7, 12am (QLD/NSW/ACT/Vic/Tas)
The Eta Aquariids are possibly the year’s most overlooked treat, particularly for observers in the southern hemisphere. The first of two annual showers produced by comet 1P/Halley, the Eta Aquariids produce excellent rates for a whole week around their peak.
The radiant rises in the early hours of the morning, after the forecast maximum time, and best rates are seen just as the sky starts to brighten with the light of dawn. It can be well worth rising early to observe them, as rates can climb as high as 40 to 50 meteors per hour before the brightening sky truncates the display.
Eta Aquariid meteors are fast and often bright, and the shower regularly rewards those who are willing to rise early. Spectacular Earth-grazing meteors that tear from one side of the sky to the other can be seen shortly after the radiant rises above the horizon.
This year conditions are ideal to observe the shower, with New Moon falling on May 4, just two days before the forecast maximum. As a result, the whole week around the peak will be suitable for morning observing sessions, giving observers plenty of opportunity to see the fall of tiny fragments of the most famous of comets.
Southern Delta Aquariids, Piscis Austrinids and Alpha Capricornids [N/S; S favoured]
In most years, the approach of August is heralded by keen meteor observers as the build up to the Perseids – the second of the year’s big three showers. This year, moonlight will interfere, spoiling them for most observers.
But this cloud comes with a silver lining. A fortnight or so before the peak of the Perseids, three relatively minor showers come together to provide an excellent mid-winter show for southern hemisphere observers. This year, the Moon is perfectly placed to allow their observation.
These three showers – the Southern Delta Aquariids, Alpha Capricornids and Pisces Austrinids – favour observers in the southern hemisphere, though they can also be observed from northern latitudes.
Regardless of your location, the best rates for these showers are seen in the hours after midnight. Reasonable rates begin to be visible for southern hemisphere observers as early as 10pm local time.
The Southern Delta Aquariids are the most active of the three, producing up to 25 fast, bright meteors per hour at their peak, which spans the five days centred on July 30.
The Alpha Capricornids, by contrast, produce lower rates typically contributing just five meteors per hour. But where the Southern Delta Aquariids are fast, the Alpha Capricornids are very slow meteors and are often spectacular.
Like the Alpha Centaurids, in February, they have a reputation for producing large numbers of spectacular fireballs. This tendency to produce meteors that are both very bright and also slow moving makes them an excellent target for astrophotographers, as well as naked-eye observers.
Active: September 10 – December 10
Maxima: October 10 (Southern Taurids); November 13 (Northern Taurids)
The Taurids are probably the most fascinating of all the annual meteor showers. Though they only deliver relatively low rates (approximately five per hour from each of the two streams, north and south), they do so over an incredibly long period – three full months of activity.
In other words, the Earth spends a quarter of a year passing through the Taurid stream. In fact, we cross the stream again in June, when the meteors from the shower are lost due to it being exclusively visible in daylight.
So a third of our planet’s orbit is spent ploughing through a broad stream of debris, known as the Taurid stream. In total, the Taurid stream deposits more mass of meteoric material to our planet’s atmosphere than all of the other annual meteor showers combined.
So vast is the Taurid stream that there is speculation that it originated with the cataclysmic disintegration of a super-sized comet, thousands or tens of thousands of years in the past, and that the current shower is a relic of that ancient event.
Taurid meteors are slow, and are often spectacularly bright. Like the Alpha Capricornids, they have a reputation for producing regular fireballs, making them another good target for the budding astrophotographer.
Rather than having a single, sharp peak, Taurid activity stays at, or close to, peak rates for the best part of a month, between the maxima of the northern and southern streams, meaning that it is always possible to find some time when moonlight does not interfere to observe the shower.
Active: December 4 – December 17
Maximum: December 14, 6:40pm UT = December 15, 4:40am (QLD) = December 15, 5:40am (NSW/ACT/Vic/Tas)
Another of the big three annual meteor showers, the Geminids are probably the best, with peak rates in recent years exceeding 140 meteors per hour.
The Geminids are visible from both hemispheres – although the radiant rises markedly earlier for northern observers. Even in the south of Australia, the radiant rises well before midnight, giving all observers the rest of the night to enjoy the spectacle.
Moonlight will seriously interfere with the peak of the shower this year, washing out the fainter meteors, with the result that observed rates will be lower than the ZHR might otherwise suggest.
But the shower regularly produces abundant bright meteors, and yields such high rates that it is still well worth checking out, even through the glare of the full Moon.
The final shower of the year – the Ursids – is a treat for northern hemisphere observers alone. Much like the shower that started our journey through the year, the Quadrantids, the Ursids remain poorly observed, often lost to the bleak midwinter weather that plagues many northern latitudes.
But if skies are clear the Ursids are visible throughout the night, as their radiant lies just 12 degrees from the north celestial pole. As such, they make a tempting target for observers to check out in the evening, even if the radiant is at its highest in the early hours of the morning.
Most years, the Ursids are a relatively minor shower, with peak rates rarely exceeding ten meteors per hour. They have thrown up a few surprises over the past century, with occasional outbursts of moderately-fast meteors yielding rates up to, and in excess of, a hundred meteors per hour.
While no such outburst is predicted for 2019, the Ursids have proven to be a shower with a surprise or two left to show and so may just prove to be an exciting way to end the meteoric year.
If you have a good photo of any of this year’s meteor showers that you’d like to share with The Conversation’s readers then please send it to email@example.com. Please include your full name and the location the photo (or any composite) was taken.
Preparations are already underway for missions that will land humans on Mars in a decade or so. But what would people eat if these missions eventually lead to the permanent colonisation of the red planet?
Once (if) humans do make it to Mars, a major challenge for any colony will be to generate a stable supply of food. The enormous costs of launching and resupplying resources from Earth will make that impractical.
Humans on Mars will need to move away from complete reliance on shipped cargo, and achieve a high level of self-sufficient and sustainable agriculture.
The recent discovery of liquid water on Mars – which adds new information to the question of whether we will find life on the planet – does raise the possibility of using such supplies to help grow food.
But water is only one of many things we will need if we’re to grow enough food on Mars.
What sort of food?
Previous work has suggested the use of microbes as a source of food on Mars. The use of hydroponic greenhouses and controlled environmental systems, similar to one being tested onboard the International Space Station to grow crops, is another option.
This month, in the journal Genes, we provide a new perspective based on the use of advanced synthetic biology to improve the potential performance of plant life on Mars.
Synthetic biology is a fast-growing field. It combines principles from engineering, DNA science, and computer science (among many other disciplines) to impart new and improved functions to living organisms.
Not only can we read DNA, but we can also design biological systems, test them, and even engineer whole organisms. Yeast is just one example of an industrial workhorse microbe whose whole genome is currently being re-engineered by an international consortium.
The technology has progressed so far that precision genetic engineering and automation can now be merged into automated robotic facilities, known as biofoundries.
These biofoundries can test millions of DNA designs in parallel to find the organisms with the qualities that we are looking for.
Mars: Earth-like but not Earth
Although Mars is the most Earth-like of our neighbouring planets, Mars and Earth differ in many ways.
The gravity on Mars is around a third of that on Earth. Mars receives about half of the sunlight we get on Earth, but much higher levels of harmful ultraviolet (UV) and cosmic rays. The surface temperature of Mars is about -60℃ and it has a thin atmosphere primarily made of carbon dioxide.
Unlike Earth’s soil, which is humid and rich in nutrients and microorganisms that support plant growth, Mars is covered with regolith. This is an arid material that contains perchlorate chemicals that are toxic to humans.
Also – despite the latest sub-surface lake find – water on Mars mostly exists in the form of ice, and the low atmospheric pressure of the planet makes liquid water boil at around 5℃.
Plants on Earth have evolved for hundreds of millions of years and are adapted to terrestrial conditions, but they will not grow well on Mars.
This means that substantial resources that would be scarce and priceless for humans on Mars, like liquid water and energy, would need to be allocated to achieve efficient farming by artificially creating optimal plant growth conditions.
Adapting plants to Mars
A more rational alternative is to use synthetic biology to develop crops specifically for Mars. This formidable challenge can be tackled and fast-tracked by building a plant-focused Mars biofoundry.
Such an automated facility would be capable of expediting the engineering of biological designs and testing of their performance under simulated Martian conditions.
With adequate funding and active international collaboration, such an advanced facility could improve many of the traits required for making crops thrive on Mars within a decade.
This includes improving photosynthesis and photoprotection (to help protect plants from sunlight and UV rays), as well as drought and cold tolerance in plants, and engineering high-yield functional crops. We also need to modify microbes to detoxify and improve the Martian soil quality.
These are all challenges that are within the capability of modern synthetic biology.
Benefits for Earth
Developing the next generation of crops required for sustaining humans on Mars would also have great benefits for people on Earth.
The growing global population is increasing the demand for food. To meet this demand we must increase agricultural productivity, but we have to do so without negatively impacting our environment.
The best way to achieve these goals would be to improve the crops that are already widely used. Setting up facilities such as the proposed Mars Biofoundry would bring immense benefit to the turnaround time of plant research with implications for food security and environmental protection.
So ultimately, the main beneficiary of efforts to develop crops for Mars would be Earth.
That brings the tally for Jupiter to a whopping 79, the most moons for any known planet. But where did these newly discovered moons come from, and what do they tell us about Jupiter and its place in the Solar system?
Moons: regular and irregular
The Solar system’s giant planets have two types of moon: regular and irregular.
Regular moons orbit close to their host, follow nearly circular paths, and move in the same plane as the planet’s equator. In some ways, these moons resemble miniature planetary systems, and we think that they formed in much the same manner as the planets around the Sun.
As the giant planets gathered material from the disk of gas and dust that surrounded the young Sun – a process known as accretion – they were surrounded by their own miniature disks. Within those disks, the regular moons grew, all in the planet’s equatorial plane.
But the irregular moons are another story.
Their orbits are highly eccentric (elliptical) and inclined relative to the plane of their host planet’s equator. Many even move on retrograde orbits, travelling in the opposite direction to the spin and orbital motion of their hosts. And they are located much farther from their planet than their regular cousins.
We think that each giant planet captured just a handful of irregular moons – a number far smaller than we see today. Over the billions of years since, those moons were pummelled and destroyed by passing asteroids and comets, and collisions with other members of their swarm.
The shattered fragments of those ancient satellites form families of smaller moons – the irregulars we see today. For example, among Jupiter’s satellites we see at least four distinct families of irregular moons, each named after their largest member.
What does the new discovery add to our understanding?
If we consider Jupiter’s moons in terms of their orbital distance, and the direction in which they move, we can break them into three distinct groups.
The first consists of the inner eight moons, including the famous Galilean moons Io, Europa, Ganymede and Callisto, whose orbits lie in the plane of Jupiter’s equator, at distances less than 2 million kilometres.
The second group lies significantly farther from the planet, and move on orbits tilted by between 25° and 56° relative to Jupiter’s equator. These are the prograde irregulars – ten moons orbiting at distances between 7 million and 19 million km. Two of the new discoveries are members of this group.
The final and most populous group is the retrograde irregulars – 60 moons located between 19 million and 29 million kilometres from Jupiter, all moving on orbits inclined by between about 140° and 170° to Jupiter’s equator.
In other words, they orbit backwards, in the opposite direction to everything else. Nine of the new discoveries fall into this category.
So that covers 11 of our new moons. What of the 12th? Well, it turns out that the most exciting of the new moons is an oddball – an object that does not fit into any of the groups mentioned above.
The oddball: Valetudo
The 12th new moon has tentatively been named Valetudo, after Jupiter’s mythological great granddaughter.
Valetudo is the dimmest of the newly discovered moons. At just a kilometre in diameter (or less), it is the smallest Jovian moon found to date.
In terms of its orbital distance, Valetudo lies bang in the middle of the retrograde irregulars – some 24 million kilometres from the giant planet. But its orbit is prograde – meaning that it moves in the direction of Jupiter’s rotation, and in the opposite direction to all other satellites in its vicinity.
Valetudo’s size and unusual orbit pose interesting questions.
How did something so small survive in the celestial firing range around Jupiter?
Could Valetudo be the final surviving remnant of a previously uncharted family, whittled to nothing by aeons of headlong flight into the retrograde irregulars?
Are there are other members of the Valetudo family out there, awaiting discovery?
Beyond these questions, Valetudo’s small size offers an important clue to the origin of the Jovian satellite system. Had Valetudo been on its current orbit while Jupiter was still accreting, it would have been too small to resist the drag of the inflowing gas. Like a ping pong ball in a gale, it would have been dragged inwards, to be devoured by the giant planet.
In other words, tiny Valetudo tells us that the process that created the irregular satellite families continued long after the formation of Jupiter was complete. In fact, that process likely continues even now, with occasional collisions tearing moons asunder, to birth new families of irregular worlds.
Who knows? The next such collision might come when Valetudo runs into one of the retrograde irregulars. Given that their orbits cross, it may only be a matter of time.
When we look up at Mars in the night sky we see a red planet – largely due to its rusty surface. But what’s on the inside?
Launching in May, the next NASA space mission will study the interior of Mars.
The InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) spacecraft will be a stationary lander mission that measures seismic activity on Mars (often referred to as marsquakes) as well as interior heat flow.
By listening to and probing the Martian crust and interior, the project aims to understand the formation and evolution of Mars.
The InSight mission is scheduled to launch from California in early May, with landing on Mars planned for November. The expected lifetime of the mission is at least two years.
Origins of marsquakes
The payload on board InSight includes the seismic instrument SEIS (Seismic Experiment for Interior Structure). Its task is to record seismic activity, or vibrations, of the planet.
Apart from shaking the ground while passing, seismic waves can be extremely useful in telling us about the structure of planetary interiors. Seismic waves travel at different speeds when passing through different materials. Processing their arrival time and strength via recorded seismographs is a clever way to learn about the interior structure of a planetary body – such as the crust, the next layer down (the mantle), and the core.
Seismic activity on Mars could be caused by a number of processes. For example, shallow marsquakes could originate from meteoroid strikes, and deep marsquakes could come from martian tectonic activity (the movement of tectonic plates at the surface of the planet).
It is generally believed that tectonic processes could have shaped Mars in its early evolution, similar to the Earth. However, unlike the Earth in younger ages, Mars has become largely tectonically dormant.
We think lots of meteoroids hit Mars
Considering that tectonics on Mars may not be reminiscent of what we see on our planet, we suspect that meteoroid strikes will play a major role in causing marsquakes.
On Earth, frequent and small meteoroids most often burn up in the atmosphere and appear to us as a form of “shooting star”. When a rock from space moving at supersonic speed encounters the terrestrial atmosphere, the air in front of it gets compressed extremely quickly. Temperature rises and heat builds up, so the rock starts to shine bright under the process of its destruction.
However, on Mars we think that meteoroids may not necessarily burn up entirely upon encountering the martian atmosphere. This is simply because Mars has a less dense atmosphere than the Earth – so incoming meteoroids have a higher penetrating power. These impact events would produce seismic disturbance in the atmosphere, and also likely in the ground.
Detecting meteoroid strikes on planetary bodies began with the lunar Apollo program. Apollo missions carried seismometers to the Moon, and as a result we had a network of seismometers that operated on the Moon from 1969-77.
During its lifetime, the Apollo seismic network recorded shallow quakes produced by frequent meteoroid bombardment. Considering that the Moon does not have an atmosphere to protect its surface from the incoming meteoroids, the Apollo seismic network provided heaps of seismic data from the Moon. These impact-induced seismic moonquakes provided the first constraints about the thickness of the lunar crust as well as structure of crust and deep interior.
We’ve tried to measure Mars seismic activity before
During the lunar exploratory boom with the Apollo program, NASA also launched Vikings 1 and 2 to Mars in 1975. These became the first missions to land on Mars, and each Viking mission carried a seismometer.
While instruments on Viking have collected more data than expected, the seismometer on Viking Lander 1 did not work after landing. The seismometer on Viking Lander 2 demonstrated poor detection rates, with no quakes coming off the ground (as it had remained on the Lander).
To date, we have had no other seismic station on any extraterrestrial planetary body. This makes InSight the first-of-its-kind mission to be placed on Mars. While its design relies on proven technologies from past missions, it is ground-breaking in terms of expected science goals.
Instead of making orbital remote sensing surveys or roving on the surface similar to other rovers, InSight has a different goal to previous Martian missions.
Why are we so interested in the subsurface of Mars?
Mars and Earth differ in size, temperature, and atmospheric composition. But similar geological features such as craters, volcanoes, or canyons can be observed on both planets. This implies that the interior of Mars may be similar to Earth’s.
It is also quite likely that there was liquid water on the surface of ancient Mars, which was the time Mars could have been very similar to Earth. So Mars could answer questions about the ancient habitability of our solar system.
Unlike potentially habitable planets orbiting distant stars, Mars is reachable within our lifetime. Discovering martian crustal properties is of great importance when it comes to planning landing missions and investigating signs of extraterrestrial habitability.
My role in the InSight mission is to work with the science team in analysing the data (impact-induced seismograms and any respective orbital imagery) to work out what kind of impacts had occurred during the mission lifetime.