Postcard from the Moon

One morning, not many weeks ago, a postcard floated gently through my letter box, onto my doormat, and brought a smile to my face. For we all know that I love me a postcard. This specimen—sent by two friends/colleagues (the indomitable duo Paul Byrne and Christian Klimczak)—was especially exciting, however, because it could almost have come from the Moon. And we all know that I love me some Moon.

My very own postcard from the Moon, or at least from the Craters of the Moon National Monument, Idaho. "Violent eruptions in the recent past have created an unearthly landscape where visitors can walk to the top of the cinder cone, hike over lava flows, or drop beneath the surface into the large caves known as lava tubes."
Original image credit: Dave Clark Photography

And at first glance (if you ignore the clouds in the very Earthly blue sky), the landscape does look vaguely lunar. We can compare and contrast: 

Lunar landscape, captured during the Apollo 17 mission. Credit: NASA

But, alas, my postcard does actually have a terrestrial origin. Rather than bearing a lunar postmark, it was sent from the Craters of the Moon National Monument and Preserve in Idaho, where my friends were carrying out fieldwork. The protected region is volcanic in nature and a presents a well-preserved example of flood basalts (another example of flood basalts—the extensive Siberian Traps—featured in one of my early postcards). The site encompasses three major lava fields (about 1000 km² in area) that include a huge variety of basalts (in terms of composition) and excellent examples of many different volcanic features (such as lava tubes and scoria cones). 

When I asked Paul why he and Christian chose this site for their fieldwork, he replied that it includes "some neat interactions between volcanic and tectonic structures (e.g., scoria cones riven by fissures, fractures, and a rift zone). Mainly we went to see what these features look like and how they might compare with similar landforms on Mars." In particular, he noted that they found "a bunch of pit craters" that look very similar to those we see on Mars. As planetary geologists, Paul and Christian are thus interested in studying the terrestrial Craters of the Moon region as a planetary analogue, i.e., to gain better insight into the similar-looking features on Mars and elsewhere.

A pit crater (about 130 m in diameter) on Mars. This example lies on the flanks of the volcano Elysium Mons. The dark pit crater is clearly different from the many surrounding small impact craters that are covered by dust and sediment. Credit: NASA/JPL-Caltech/Univ. of Arizona

A pit crater, like a sinkhole, is a depression that forms via the collapse of a surface overlying an empty chamber. Unlike impact craters that have raised rims and sloped walls, pit craters have steep/almost vertical walls. In planetary imagery they thus appear as dark, approximately circular, shadowed holes, and their floors can only be seen when the Sun is at a high angle of illumination. One way that a pit crater may form—especially in volcanic environments—is through the collapse of a lava tube (which is essentially a tunnel formed by lava flowing underground). This process may begin with the buckling of the tube's roof at a location where the roof is thinnest. These craters are often known as 'skylights' because light can flood through them into the darkness of the connected cave.

In 2007, such skylights were discovered on Mars. Scientists looking at the pictures form NASA's Mars Odyssey and Mars Global Surveyor satellites were puzzled by the very dark, circular features. By combining the images with thermal information from Mars Odyssey's infrared camera, however, they concluded these pits were indeed windows into underground caves. Soon after, in 2009, the first lunar skylight discovery was made by a team working on high-resolution images returned from the Japan Aerospace Exploration Agency's SELENE satellite. 

High-resolution image from NASA's Lunar Reconnaissance Orbiter Camera showing a 'skylight' in the Moon's Mare Ingenii region. This pit has a diameter of about 130 m.
Credit: NASA/Goddard/Arizona State University 

These skylight discoveries have got many in the planetary science community quite excited. It is thought that the subsurface structures they provide a window into, could provide a potentially habitable environment. On Mars, organisms could have perhaps flourished under the protection of the ancient lava tubes (i.e., acting as a shield against harmful ultraviolet radiation). Moreover, if the lava tubes are structurally stable at a large enough size, they could be suitable as shelters for human explorers. Indeed, the maximum potential diameter of lunar lava tubes has been estimated by yet another friend/colleague of mine. While a PhD student at Purdue University, David Blair led a study in which he calculated the stresses and strains that would be present around lunar lava tubes. Given the size of the lava tubes inferred from NASA's GRAIL gravity data (i.e., with diameters of more than 1 km), the team estimated that the structures could remain stable even at widths of more than 1.6 km.

The Indian Tunnel lava tube in Craters of the Moon National Monument and Preserve. This tube is about 9 m high, 15 m wide, and 245 m long. Lava tubes on the Moon are thought to be substantially larger because of the reduced gravity. Credit: Kurt Allen Fisher/Universities Space Research Association.

If Dave and his team are right, these lava tunnels may one day present a useful extraterrestrial habitat for humans—big enough to house sizable settlements. When living here on Earth is no longer feasible, perhaps we will decamp as a race to the lunar lava tubes where we will shelter from the bombardment of radiation and escape temperature extremes. I think we can therefore justify sending a piece of (basaltic) rock from the Craters of the Moon for this Postcard From Planet Earth. As a terrestrial analogue for these potentially habitable extraterrestrial settings, it can be our message to the alien planetary geologists when they arrive for their inevitable visit: 'if we're not in, try elsewhere'.

A whole world's wake-up call

The past few weeks in the world of space have been pretty hectic. Most especially because of the fantastic new views of Pluto we've been receiving, courtesy of the New Horizons flyby (which I wrote about in my last postcard). We've also been hearing about the "frozen primordial soup" of organic compounds detected by the European Space Agency's Philae lander on comet 67P/Churyumov–Gerasimenko, as detailed in a new special issue of Science. Some of these compounds may be important for the prebiotic synthesis of amino acids, sugars, and nucleobases, i.e., the very ingredients of life. 

The surface of comet 67P/Churyumov–Gerasimenko, as imaged from 9 metres away. Credit: ESA

But there are two other recent news items I want to focus on in this postcard. First, the new photograph of the Earth captured by NASA's new Deep Space Climate Observatory (DSCOVR) satellite. And second, the recent discovery of an exoplanet that is being billed as Earth's 'twin'.

On 6 July 2015, the Earth Polychromatic Imaging Camera (EPIC) instrument on DSCOVR returned its first view of the entire sunlit Earth. Safe in its gravitationally stable location one million miles away—at a so-called Lagrange point—the satellite was able to obtain this kind of full-Earth portrait for the first time since the famous 'Blue marble' photograph was snapped by the Apollo 17 astronauts whilst on their way to the Moon in 1972. I've mentioned that older, stunning photo in a previous postcard, but as the most reproduced image in history, I think that it is more than worth showing again.

The famous and historic 'Blue marble', taken during the Apollo 17 mission in 1972. Credit: NASA

It might come as a surprise that it has taken more than 40 years to recapture Earth in a similar view. The pictures you've seen of Earth's full disc in the meantime have either been this Apollo 17 photograph, or composite images (i.e., several smaller images that have been stitched together). It is difficult to obtain these images because many variables come into play. The camera must be between the Earth and the Sun, and far enough away to capture the whole planet in its field of view. Although weather satellites—in geosynchronous orbits—get similar views, they cannot normally see an entire hemisphere without shadow.

The Earth, from one million miles, as seen by the Deep Space Climate Observatory on 6 July 2015. Credit: NASA

The data from EPIC will primarily be used to measure changes to the ozone and aerosol levels in Earth's atmosphere, as well as cloud height, vegetation properties, and ultraviolet reflectivity characteristics. But these new, beautiful, images of a whole Earth remind us how powerful it is to see our entire home in one go. As pointed out by John Grunsfeld, associate administrator of NASA's Science Mission Directorate, "these new views of Earth give us an important perspective of the true global nature of our spaceship Earth."

Indeed, I'm reminded of an excellent book I read several years ago by Robert Poole. In Earthrise: How Man First Saw The Earth, Poole tells the story of how images of Earth—such as the Blue marble and the equally famous Apollo 'Earthrise'—taken during the dawn of the space age, played a huge role in the birth of the now-popular environmental and conservation movements.

'Earthrise' photograph taken by astronaut Bill Anders during the Apollo 8 mission, on 24 December 1968. Credit: NASA

It is another aspect of these images of our blue Earth, however, that strikes me most. It is the human capacity for intelligence and creativity that enables space exploration and capturing of Earth-selfies from afar. Yet we do not see evidence of our presence in these pictures. In many ways, we are invisible to the universe. It is not life that makes Earth special. It is the blue oceans, the green forests, and the white wispy clouds in our lovely oxygen-rich atmosphere that make our world habitable. So for this postcard to our hypothetical alien planetary geologists, I want to send a snapshot of our whole world. Let them see the Earth and all its systems intertwined.

The uniqueness of Earth, however, might be under threat if a new discovery from the Kepler space telescope is anything to go by. On 23 July 2014, scientists working on the Kepler mission announced that they have found the most Earth-like extrasolar planet yet. The new planet—known as Kepler-452b—is located about 1,400 light years away, and is a similar size to Earth. In addition, Kepler-452b orbits a Sun-like star at a distance that is similar to that of Earth around the Sun. The planet is being hailed as "the first possibly rocky, habitable planet around a solar-type star". And it will thus, likely, become the focus of an intense search for extraterrestrial life. Perhaps we'll even find those alien planetary geologists there waiting for us.

Artist's concept of Kepler-452b in orbit around its parent star. Credit: NASA Ames/JPL-Caltech/T.Pyle

At a time when humanity seems to be as fractured as ever, perhaps we need a wake-up call like these ones from NASA. We need to be reminded every once in a while that we are all one family, stuck together here on our little spaceship Earth. We should do our utmost to look after it—and each other.

Dark new horizons shed light on an old Earth

My last postcard was about context. In that postcard, I explained how MESSENGER's exploration of Mercury has helped us learn more about the planetary neighbourhood in which our Earth sits. And for this latest offering, I want to follow a similar theme. But first, we need to take a pretty huge leap (about 5.85 billion km) across the Solar System. Where we will find ourselves in the vicinity of Pluto.

Pluto—once famous for being the ninth and most distant planet from the Sun—is now more famous for being the planet that isn't a planet. Following its discovery in 1930, Pluto—which has a diameter of about 2,300 km—enjoyed more than 75 years at the planet level of the Solar System hierarchy. But in 2006, members of the International Astronomical Union (IAU) decided to demote Pluto, and assign it a new status as a dwarf planet. This decision was prompted when it became clear that Pluto is just one of many large, Sun-orbiting icy bodies in the outer Solar System. The astronomers therefore decided to officially define the term planet, specifically so that Pluto (and other bodies like it) would be excluded from this class.

Photographic plates used for the discovery of Pluto. The arrows mark Pluto's position. Pluto clearly moved against the background of stars in the six days between the two observations, which were made by Clyde Tombaugh in 1930. Credit: Lowell Observatory Archives

Under the IAU's new formal definition, a planet must meet three requirements:

1. The celestial body must orbit the Sun.
2. The body must have a large enough mass to give it a nearly round shape. 
3. The body must have cleared the neighbourhood (of other material) of its own orbit.

Unfortunately—for Pluto at least—the former ninth planet could not meet this third requirement. And a global public outcry—which continues today—followed.

The International Astronomical Union's decision to reclassify Pluto and strip it of its planet status hit the headlines in 2006 and caused a huge public outcry.

But the question of Pluto's planethood is currently being pushed aside, as the level of excitement surrounding NASA's New Horizons mission rapidly grows, prior to the spacecraft's Pluto fly-by. New Horizons—first launched in 2006—is the first spacecraft to visit Pluto and its system of five known moons (Charon, Styx, Nix, Kerberos, and Hydra). The probe will not go into orbit around Pluto, but will instead zoom by a week from now, on 14 July 2015. The fly-by will only last about eight or 10 hours, but at its closest approach the spacecraft will be about 12,500 km from the surface of Pluto. 

Photograph of Pluto and its five moons taken with the Hubble Space Telescope in 2012. Credit: NASA, ESA, and L. Frattare (STScI)

The scientific payload of the spacecraft consists of seven instruments that were chosen so that the geology, surface composition and temperature, and atmospheric characteristics of Pluto and its moons could be investigated. The bulk of the scientific data will be obtained during a period of about 24 hours around the time of the fly-by. The best pictures should reveal features as small as 60 metres across on Pluto's surface.

Map of Pluto released by the New Horizons team on 7 July 2015. The map was created from images obtained with the spacecraft's Long Range Reconnaissance Imager (LORRI) instrument, which were combined with low-resolution colour data obtained with the Ralph instrument. The map clearly shows an intriguing pattern of bright and dark markings on Pluto's surface. The brightest region may contain fresh deposits of methane, nitrogen, and/or carbon monoxide frost. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

This newest installment in the history of human exploration of the Solar System is all very nice, but how is it relevant to my original brief? How can learning about this far-distant world help us convey the uniqueness of Earth to a hypothetical alien planetary geologist? Well, if all goes to plan, then the fly-by of Pluto will not be the end of the New Horizons mission. It  should just be the end of the beginning. Pending approval from NASA for an extended mission, New Horizons will be sent on an onwards journey to study another Kuiper belt object.

The Kuiper belt is a region that extends outwards from the orbit of Neptune for about 20 AU (astronomical unit, equal to about 150 million km). It is similar to the asteroid belt (which lies between the orbits of Mars and Jupiter), as it contains many—relatively small—bodies that are remnants from the formation of the Solar System. Most Kuiper belt objects are icy bodies, composed mainly of substances such as methane, ammonia, and water. Pluto is the largest known object in the Kuiper belt, but about 100,000 objects (with diameters of more than 100 km) are expected to exist in this region, and more than one thousand have been discovered since 1992.

The path of the New Horizons spacecraft (yellow line) through the outer Solar System and the Kuiper belt. The orbits of the planets are shown in blue. The largest Kuiper belt objects are labelled. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker

By studying Pluto and its Kuiper belt companions, we can potentially learn about two aspects of Earth's earliest history. As remnants of the Solar System's formation, the Kuiper belt objects are seen as akin to planetary embryos or protoplanets. Planetary accretion is believed to begin with the condensation of solids from the gas cloud that surrounds a star. Accretion of gas and dust then produces bodies that have diameters of 1–10 km, which are known as planetismals. The Kuiper belt objects can help us understand this early accretionary stage and thus what processes went into building our Earth. Violent impacts that occurred during the stage of runaway growth allowed the many planetismals to coallesce and form the large planets we know today.

In addition, the Kuiper belt is thought to be the region from which most short-period comets (i.e., those with orbits of less than 200 years) originate. As the European Space Agency's current Rosetta mission has wonderfully shown, comets are intriguing bodies in our Solar System. Indeed, many scientists believe that comets may have contributed a significant proportion of Earth's water inventory. In a previous postcard, I discussed how a Jupiter-family comet—which probably originated in the Kuiper belt—has a water signature that is a good match for that of Earth. 

New Horizons therefore provides us with a great opportunity to get to know the Kuiper belt better and to potentially understand the building blocks of Earth just a little bit more. But furthermore, the Kuiper belt may provide a big clue to any alien astronomers of our Earth's existence. Neptune, as a giant gas planet, exerts a great gravitational force on the cloud of dust that surrounds it in the Solar System (which includes the Kuiper belt). The gravity tugs on this cloud of dust and creates a distinctive ring structure. Computer simulations show that this ring contains a gap where Neptune itself resides. So even if the alien astronomers cannot directly image the planets of our Solar System from afar, they might be able to detect Neptune's presence. As such, they would know that our Sun possesses a planetary system, and we on Earth are here to be found.

Computer simulations show what the Solar System might look like to an alien astronomer. The gravity of Neptune creates this distinctive ring structure in the dust cloud. The planet itself resides in the gap that can be seen as the dark area in the right of the image. Credit: NASA/Goddard/Marc Kuchner and Christopher Stark

Requiem

Lacrimoso

Today will see the end in the life of a dear friend. A life in which I am proud to have played a small part. At the beginning of 2011 I moved across the Atlantic Ocean to Washington, D.C., to start a new job—working on the science team of NASA's MESSENGER mission. That move was one of the best decisions I have ever made. But later today, after more than four years in orbit around Mercury, and over 10 years in space, the mission is about to come to a very conclusive end. The spacecraft is now, well and truly, out of fuel. It will crash into the planet and it will form a new crater in the already pocked surface. But as I mourn the loss of our spacecraft, I can look back with pride and celebrate the wonderful achievements of this groundbreaking mission.

Artist's impression of the MESSENGER spacecraft in orbit around Mercury. Credit: NASA

MESSENGER—an acronym for MErcury Surface, Space ENvironment, GEochemistry, and Ranging—has been the first spacecraft to orbit Mercury, the innermost planet of our solar system. After more than four years of studying Mercury from orbit, MESSENGER has completely transformed our understanding of the planet. Back in the 1970s, Mariner 10—the only other spacecraft to have visited Mercury—made three flybys of the planet. Although Mariner 10 led to several important discoveries, substantial gaps were left in the Mercury cannon. Less than half the planet, for instance, was imaged up close by Mariner 10.

Mariner 10 image showing part of the Caloris basin (left), the largest well-preserved impact basin on Mercury. The basin has a diameter of about 1,550 km and its full extent was realized only during the MESSENGER mission. Credit: NASA

Following Mariner 10, many scientists believed that Mercury was geologically similar to the Moon, and therefore not worth an expensive and extensive follow-up mission. But a committed and insightful group of scientists and engineers, led by Principal Investigator Sean Solomon, were not so easily placated. They believed that Mercury could not be so easily dismissed and they set about making their MESSENGER dream a reality. The MESSENGER mission concept was finally accepted as the seventh of NASA's Discovery-class missions, in July 1999.

Several engineering challenges are presented in designing spacecraft to orbit Mercury. In addition to the extreme heating conditions the spacecraft must endure, the Sun's huge gravitational pull is a major issue. To enter orbit around Mercury, the spacecraft must be captured by the gravity of Mercury itself, which is tiny in comparison with that of our parent star. So the clever rocket scientists came up with a solution. Instead of sending the spacecraft on a direct course to Mercury, MESSENGER took a particularly circuitous route into the inner parts of the Solar System. To be captured by Mercury's gravity, MESSENGER's speed needed to be dramatically reduced as it approached the planet. But a body moving towards the Sun will be constantly speeding up. Of course, spacecraft thrusters (i.e., brakes) can be fired to reduce the velocity, but this requires a tremendous amount of fuel, and massively increases the weight and cost of launching the spacecraft from Earth. 

The gravity fields of the inner planets were therefore used as an alternative, natural, braking system. After MESSENGER was launched from Cape Canaveral on 3rd August 2004, the spacecraft undertook a series of 'gravity assist' flyby manoeuvres, which were designed to reduce its velocity. A year after launch, MESSENGER performed its first flyby, of Earth, on 2nd August 2005. Next up were two flybys of Venus in 2006 and 2007. Then in 2008 and 2009, MESSENGER made another three flybys, this time of Mercury itself, before it finally entered orbit on 18th March 2011.

 

The Earth, our home, as seen by MESSENGER during its gravity assist flyby on 2nd August 2005. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

It is images such as this one of Earth taken by MESSENGER, that remind us of the power of comparative planetology. Even with the fantastic capabilities of remote sensing, as exemplified by MESSENGER and other planetary satellites, there are certain geological investigations that can never be achieved if you do not have physical contact with a planet. The study of Earth, and the comparison of its geological features with those we observe on Mercury (and other planets), is therefore a vital part of our planetary science investigations. But furthermore, by studying Mercury (the end-member of the Solar System), we also gain a more thorough understanding of the neighbourhood in which our Earth sits.

My role in the MESSENGER mission, was as a postdoctoral fellow at the Carnegie Institution of Washington's Department of Terrestrial Magnetism. I worked with Larry Nittler on the analysis of data from MESSENGER's X-Ray Spectrometer (XRS), through which we are able to learn about the geochemical makeup of the planet's surface. In our first MESSENGER XRS paper, we analyzed data from the first three months of the orbital mission. These data provided the first glimpse of Mercury's major element composition, and showed us that Mercury's surface is not as like the Moon (or typical parts of the Earth's crust) as had previously been thought. 

Maps of magnesium/silicon and thermal neutron absorption across Mercury's surface, as measured with MESSENGER's X-ray and Gamma-Ray Spectrometers. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

It is these geochemical findings that allow theories of Mercury's formation to be constrained. In particular, scientists have long puzzled over the reason for Mercury's particularly high density (i.e., it has a disproportionately large core). Some scientists believe that the outer (and less dense) parts of Mercury were obliterated during a huge impact event early in the planet's history. The MESSENGER geochemistry results, from the XRS and the Gamma-Ray Spectrometer, however, have revealed that Mercury is not depleted in a group of chemical elements known as volatiles. These elements (including sulfur, sodium, and chlorine) should be lost (evaporated) during the heating that would have been associated with such a massive impact event.

It is more likely, think other geologists, that the major-element composition of Mercury is much more indicative of the original materials which accreted to form the planet. Perhaps those original materials had distinctive compositions, unlike the materials that built the other planets in the Solar System. In that original Science paper, we proposed materials akin to enstatite chondrite meteorites as the potential building blocks of Mercury. The jury is still out on what those precursor materials may have been. And in all likelihood, those materials may no longer exist and may not be present in our meteorite collection. But by studying Mercury in depth for the first time with MESSENGER, we have learned about the full diversity of the Solar System.

So this postcard isn't about sending a single rock from Earth to the alien planetary geologists. It is about the much bigger picture. For those aliens to really understand our wonderful home, they need to see Earth in the context of its planetary brothers and sisters. By sending spacecraft to visit Mercury, Venus, Mars, as well as the outer planets and moons of the Solar System, we are building up a panoramic postcard of our whole family.

Thank you MESSENGER for playing your part perfectly in that endeavour. You served us well and you will be missed.

The Earth and Moon, taken from the MESSENGER spacecraft at Mercury. The Earth is the bright object in the bottom-left of the image. The Moon is the smaller and fainter spot to its right. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Finis

What's up Sun?

For this postcard from planet Earth I've decided to cheat a bit on my own rules and pick a rock that isn't necessarily of the Earth, even if it is on the Earth. Mainly because I wanted to write about something close to my heart.

Let me explain.

I recently read this article in Scientific American. The research it highlights describes how interactions between solar wind and interplanetary dust particles can produce water. This got me thinking about how the Sun is a vital piece in creating our habitable little part of the solar system / galaxy / universe. (It also links nicely to my previous postcard, where I discuss how water might originally have been brought to Earth.)

The solar wind is a stream of charged particles (mostly electrons and protons) released from the Sun's upper atmosphere. This stream can vary, over time and from location to location around the Sun, in its density, temperature, and speed.

During solar flares, strong blasts of solar wind are fired through the solar system.
Credit: NASA

Now, even though I am a geologist and I spend most of my working hours thinking about rocks on planets other than our own, I also spend a fair bit of time thinking about the Sun. And worrying about the Sun.

You see, as a PhD student I waited (not necessarily patiently) for sunspots to erupt on the Sun's surface and for solar flares to fire X-rays through the solar system, towards the Moon's surface where an orbiting spectrometer onboard India's Chandrayaan-1 lunar satellite would detect the resulting X-ray fluorescence and provide me with some much needed data to analyze for my thesis research. Unluckily for me, I was doing my PhD when the mission was active, during the deepest solar minimum in over a century (solar cycles normally last about 11 years and most solar flares occur during the peaks of activity). Needless to say, my desired events were few and far between. Indeed that solar minimum lasted much longer than had been anticipated and the current cycle was almost a full year 'overdue' by the time it started.

Nowadays I still keep a watchful eye on the Sun's activity. Mostly because I work on the analysis of similar X-ray fluorescence data from NASA's MESSENGER mission that is currently orbiting Mercury. And it seems that predictions for the length and strength of the cycle change from week to week. For instance, this recent article discusses whether the Sun might be headed into another 'Maunder Minimum'. This was an approximately 70-year period (1645–1715) when the Sun was almost completely devoid of sunspots. The Maunder Minimum coincided with the middle of the Little Ice Age, during which there was a series of particularly frigid northern hemisphere winters.

Schematic illustration of MESSENGER's X-Ray Spectrometer in operation around Mercury. Credit: NASA / The Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington

The beautiful northern and southern lights, or the aurorae borealis and australis, occur when the energetic charged particles of the solar wind are directed by the Earth's magnetic field into the atmosphere at high latitudes, where they undergo collisions with atmospheric atoms. But besides acting as a long-term forecast tool for keen aurora hunters, much of today's solar physics research is focused on aspects of the Sun's activity that affect our lives here on Earth.

The magical northern lights. Credit: Bjorn Jorgensen / National News & Pictures

For example, coronal mass ejections (CMEs) occur most frequently during the peak periods of a solar cycle, and induce geomagnetic storms. Threats to Earth-orbiting telecommunication satellites in high, geosynchronous orbits are posed during these storms. The high currents that are discharged to the satellites can damage their components. Additionally, geomagnetic storms have been known to cause the temporary loss of electrical power over large regions, such the 1989 Quebec event. Understanding when and why CMEs occur can help plan for, and mitigate the effects of, geomagnetic storms on our telecommunication and electricity networks.

And some research has shown that the variable output of ultraviolet radiation through the course of a solar cycle can be tied to terrestrial climate changes. Climate scientists are now trying to make reliable climate predictions on decadal timescales, therefore sound solar predictions are important inputs for their models.

So with all this research in solar physics, why are predictions for the Sun's activity so seemingly unreliable? Physicists have observations from a host of solar satellites at their disposal, yet they seem to still be in the metaphorical dark.  Perhaps this complex problem will just a little bit longer to unravel, or maybe the timescales of study are too short?

And that's where my rule-bending rock postcard comes in.

I wonder if we can use material that the Apollo astronauts brought back from the Moon to increase the length of time over which we can study the Sun and its solar wind output. Back in 1970, scientists made measurements of noble gases (such as helium and argon) that were trapped inside tiny pieces of the lunar soil. And it is thought that those noble gases were implanted into the soil as the solar wind bombarded the Moon's ancient surface. So by studying these trapped pieces of the solar wind we can learn more about how the Sun has changed through time. If we had enough samples from discrete layers in the lunar surface we could even build up a record of this solar wind material that might help place the Sun's modern activity into a larger context and give the solar physicists a helping hand.

Color photograph of Apollo 11 lunar soil sample 10084. These grains are between 9000 and 10,000 mm. Credit: NASA / Johnson Space Center

We might still be learning and then re-learning things about our Sun, but I think it is important that we send one of these tiny Moon pebbles, complete with its trapped solar cargo, to our alien planetary geologist friends. They should know it is the Sun king who rules over us and our whole solar system. Maybe they could even help us decipher its mysteries.

Tardi and hardy space travellers

Recently, this BBC headline caught my eye:

Dinosaur asteroid 'sent life to Mars'

The piece focuses on an Astrobiology research article by Worth et al. In the paper the authors consider the likelihood that rocks ejected from Earth (or Mars) during large meteor impacts launched life-bearing materials into space. It is possible, they claim, that such rocks could reach other planets or moons in the solar system, where the life could resettle and colonize. This concept—known as lithopanspermia—isn't new, but their statistical approach to the problem is.

Back in 1996 a meteorite found in Antarctica, but which originated from Mars, known as Allan Hills 84001 (ALH 84001) hit the news. NASA scientists claimed that this rock contained evidence of life once having existed on Mars.

Electron microscope image of 'fossilized microbes' in the Allan Hills 84001 meteorite. Credit: NASA

Obviously this controversial subject has been disputed ever since and it has been shown that all the rock's 'biosignatures' can be produced inorganically, i.e., without the need to invoke life.

Whether or not this particular meteorite contains ancient martian lifeforms, it prompts an interesting question that links back to the subject of lithopanspermia. Is it possible for life from Earth to be exported? If we were to pick an organism to undertake this journey, what would it be? And what rock would we encase this organism in, to try and ensure its survival?

I've never been a big fan of bugs, in fact I'm pretty terrified of anything with more than four legs. However, I recently became aware that a group of organisms known as tardigrades exist. And even I have to admit that these little monsters are cool.

A tardigrade in moss. Credit: Eye of Science / Science Source Images

Tardigrades are classified as extremophiles, organisms that can survive in some of Earth's most difficult conditions. But these guys take the term to the extreme—they're pretty much indestructible. They can withstand temperatures that range from just above absolute zero to more than the boiling point of water, pressures greater than at the deepest ocean trenches, and the vacuum of space along with its harsh radiation conditions. So my vote goes to the tardigrades as the space-faring guinea pigs that get to be sent on a one-way (and potentially suicidal) mission to somewhere.

The encasement of rock around our tardigrades must also be chosen carefully. The material needs to be strong enough to survive two impacts: the large meteor event that expels the material into space, and the sample landing on the surface of its destination. Hardy quartzite, the metamorphic product of simple sandstone, would probably be a good option. Or perhaps a material similar to that of ALH 84001, i.e., an igneous rock called orthopyroxenite, would meet the requirements.

I don't know if life on Earth originated through lithopanspermia, or if life exists elsewhere because of it, but I do quite like the idea of the hardy tardigrades ruling some distant planet.