First historic report of death by meteorite located There have been documented cases of stones falling from the sky for centuries. However, even though one stone fell through the roof and hit a sleeping woman in Alabama, and one piece of a martian meteorite is famously reported as having killed a cat, until today there were no known cases of a meteorite actually killing someone. This map, with a few details added by modern authors, shows the suspected track of a meteorite that entered the Earth’s atmosphere above what is today Iraq in 1888. The rock entered the atmosphere and as the atmosphere slowed the rock, it heated up and built so much pressure that eventually it triggered an explosion – an airburst. A just-published paper demonstrates that after this event, 3 independent documents were generated stating that fragments of this exploding rock killed one man and paralyzed another. Those documents were delivered to the Sultan of the Ottoman Empire at the time and have been stored in files in Turkey ever since, until these researchers uncovered them. The researchers suggest that there are likely other cases of people killed by rocks falling from space that have been stored in document vaults around the world, waiting to be recognized today. -JBB Image source and original paper: https://onlinelibrary.wiley.com/doi/epdf/10.1111/maps.13469

As part of preparations for Launch, the Perseverance Rover this week was loaded onto this 3-D rotation table, which spins it around such that its center of mass could be measured. To make sure the rover is fully balanced for its space trip, small amounts of additional mass were added to move the center of mass almost exactly where it was supposed to be in the launch and entry/descent/landing planning.

Original caption:

Jupiter the Destroyer

We should be thankful that the early solar system was not conducive for life. During those early days, Jupiter was less constrained by its current orbit and swung through the early solar system, annihilating a first generation of inner planets, according to studies of planetary dynamics.

Based on a simulation of early planetary formation, the destructive behavior of an adolescent Jupiter may explain why our solar system has so little in common with other planetary systems. In these other systems, large rocky planets orbit extremely close to their host star — much closer than the distance between Mercury and the Sun. Jupiter's wanderings is a possible reason to our solar system's lack of inner rocky planets.

After the planetary apocalypse, Jupiter eventually settled into its current orbit, while the much of the debris of these first generation planets plunged into the Sun. The remnants that did not suffer a fiery fate would eventually coalesce into the modern inner planets of Mercury, Venus, Earth, and Mars — another reminder that we are nothing more than the recycled remains of our planetary progenitors.

-DC

Original PNAS paper: http://bit.ly/1CNpgOI

Further reading: http://bit.ly/19NYGtC http://bit.ly/1ComHlG http://bit.ly/1IsQbzA

Photo credit: http://bit.ly/1Gh53Sv

Lunar Lava Tubes

Lava tubes are sub-surface volcanic tunnels. These structures form on surfaces sloping 0.4-6.5 degrees when a roof of basaltic lava (up to 40m thick) hardens over molten rock below. This molten rock eventually drains away leaving a hollow structure. These structures also form on Earth as seen in Iceland, Portugal, Spain and the USA, however it is thought they would be larger on the moon due to its lower gravity.

This picture shows a 50km chain of collapse tunnels moving into an un-collapsed example of a lunar lava tube. In 2008 the Japanese spacecraft Kaguya sent back a picture of a suspected opening to a lava tube from the Marius Hills region (a noted lunar volcanic province). This structure was circular and approximately 65m in diameter and estimated to be 85m deep. Surrounding the hole on the lunar surface was a thin lava sheet which may have protected the tube from collapsing previously due to impacts. From 2009 onwards NASA’s Lunar Reconnaissance Orbiter also sent back pictures of deep caverns on the moon which had potential to be collapsed lava tubes.

It is thought that lava tubes would offer an environment to build a base for humans on the moon due to the protection they would offer. There would be three major factors such a tube would protect a human base from. Firstly caverns with roofs thicker than 10m would create a more stable temperature (of about -20 degrees C) than is found on the lunar surface, which varies by 100s of degrees C in a day. Secondly the moon also has no atmosphere, so these tubes would provide protection from cosmic radiation. Finally protection from meteorites, micrometeorites and collision ejecta would be offered (however it should be noted that stable lava tubes could be disrupted by seismic events and meteorite strikes).

It has been structurally modelled that tubes would be stable when sized between 1 and 5km wide and therefore could host a pre-fabricated base. The building of this base in the tube would be beneficial as lightweight construction material could be used as it would not have to shield the base from the threats mentioned above. ~SA

Pictures: http://bit.ly/1MRgf85 By NASA/GSFC/Arizona State University and http://bit.ly/1H6pWRN By Melissausburn

One day the Earth might copy its gas-giant cousins and garner a ring system of its own. The ring’s origin? Why, from our own moon, of course.

The Earth and the Moon exert gravitational forces on each other, which we witness in the form of tides when oceanic boundaries meet continental terrain. However, the tides we experience travel ahead of the Moon’s position because the rate of the Earth’s rotation differs from the rate at which the Moon orbits Earth (~24 hours vs. ~27 days). In doing so, the Earth transfers rotational energy to the Moon. Consequentially, the Earth’s rotation slows (lengthening the “Earth-day”), and the energy transferred to the Moon causes its rotational energy to accelerate, pushing its orbit further away.

Eventually the Moon will orbit the Earth at the same rate as which the Earth rotates. Then the Moon will only be visible over one region of the earth. Tides will no longer ebb and flow, but remain in fixed positions with respect to this configuration.

Yet when the Earth’s rate of rotation slows to more than that of the Moon’s orbit, the Sun’s gravitational influence will upset their balance. The gravitational force of Earth-Sun tides will begin to pull the Moon closer to Earth again. Several billion years later, the Earth’s gravitational influence on the Moon will be so strong that it tears the Moon apart. Fragments of the Moon would then orbit Earth in a ring system, as envisioned above.

Sources: http://www.bbc.com/news/science-environment-12311119

http://www.psi.edu/epo/faq/earth_moon.html

Photo Credit: PSI

Alien Hot Springs

One of the biggest discoveries of NASA's Cassini spacecraft was the presence of geothermal activity in an ocean on one of Saturn’s moons - Enceladus.

We've known about ice on Enceladus for several decades, but the freezing temperatures on the surface (highs of -198ºC) seemingly made life there extremely unlikely. But, back in 2005 Cassini saw giant plumes of water vapour coming from Enceladus' south pole, erupting up to 30km from the surface. This observation  told us that somewhere in Enceladus there was enough heat to create liquid water - the vital ingredient for life. Gravitational measurements of Enceladus have since revealed that there could be an ocean up to 10km deep underneath the moon's icy surface - comparable in size to one of Earth’s great lakes. This upgraded Enceladus from a frozen wasteland, to one of the most promising places in our solar system to look for alien life. During the observations of Enceladus, the Cassini Spacecraft sampled some of the water ejected by flying through the plumes and measured the spectral signatures of the material to look for trace components that can give information about what is happening at depth in the ocean. Using a combination of Cassini's observations, laboratory experiments and basic chemical and physical principles, scientists were able to show that these particles must have come from active hot-springs, deep in Enceladus' oceans.

So what's all the fuss about? We're not talking about a photo of E.T. relaxing in a Spa here, so why has this got the extra-terrestrial crowd so excited? Hot-springs, or hydrothermal vents, are present throughout the deep ocean on Earth. They are remarkable because, despite existing in the pitch-black ocean depths, they are teeming with life. The scorching hot water (up to 400ºC) and minerals spewing from the vents provides all the energy this ecosystem needs. Many researchers think that life on Earth began at hydrothermal vents.

Finding them on Enceladus is exciting because it means that this small, icy moon has liquid water, heat and vigorous chemical reactions: all the ingredients for life. This could mean that bacterial life, and possibly more complex organisms, could exist there.

The moon Titan of Saturn is also thought to have an ocean beneath its surface, although there are not huge sites where this ocean is being ejected to the surface as on Enceladus. NASA recently announced that it will fund and begin building a new spacecraft to fly to Titan called Dragonfly - capable of hopping around Titan’s surface and looking at the chemistry of various spots. 

Image Credits: - Enceladus plumes: NASA/JPL-Caltech - Hydrothermal Vent: IFE, URI-IAO, UW, Lost City Science Party; NOAA/OAR/OER; Lost City 2005 Exp./CC BY 2.0 Nature News Feature: http://goo.gl/sKpsqw A hydrothermal vent (video): http://goo.gl/NgIK7a Did life evolve at vents?: http://goo.gl/X7I69w More about Cassini's trip to Saturn: http://goo.gl/jTqmx Original Article: http://goo.gl/ietceh

The Last Great Impact and the Birth of Our Moon

We recently published a post about how important the Moon is to our existence (http://on.fb.me/1vSgIix), but have you ever considered how our moon first formed? While there are several hypotheses, the ‘Giant Impact Hypothesis’ is currently the most favoured.

It is proposed that a protoplanet the size of Mars (often referred to as Theia) struck the newly formed Earth 4.5 billion years ago. The debris from this event began to coalesce and out of the destruction rose our Earth and a brand new Moon. However, it was George Darwin in 1898 who first proposed that the Moon and Earth may have originated as the same body. He proposed the Moon was formed from centrifugal forces spinning off molten material from the Earth.

Using Newtonian mathematics he concluded that the Moon had orbited much closer to the Earth in the past and was actually drifting away with an ever increasing orbit. This idea was bolstered when both American and Soviet experiments confirmed that the Moon was in fact moving away.

Despite his best efforts George Darwin could not create a mathematically sound reconstruction of how the Moon first separated from the Earth’s surface. It was not until 1946 that Reginald Aldworth Daley of Harvard University proposed an alternative theory to that of centrifugal forces. Could an impact have separated the Earth and Moon?

Little attention was paid to Daley’s ideas and it wasn’t until 1974 at a conference on satellites that the idea was brought back to light. In 1975 Dr William Hartmann and Dr Donald Davis published a book called Icarus, in which they suggested that a satellite sized body could have collided with Earth ejecting enough material to form the Moon.

The key piece of evidence supporting the giant impact hypothesis is the geochemical analysis of lunar rock collected during the Apollo 11, 12 and 16 missions. If the Moon formed purely from the Earth then Earth rocks and lunar rocks would be expected to show the same geochemical abundances.

If the Moon had formed elsewhere in the solar system to become later entrained within the Earth’s gravitational field, then there would be no similarities in rock samples.

The results indicated that the samples were different enough not to have formed from the same material, but showed similarities that disputed the idea of the moon having formed in a separate part of the solar system.

Lunar rocks show relative depletions in volatile molecules such as water, which have low boiling points. In fact there are more water in bones than on the moon. It is suggested that the heat from a giant impact would have evaporated any volatile present and, as the Moon formed from the debris, that it inherited the deficiency in these molecules.

However, some have suggested that the similarities between Lunar and Earth rocks works to discredit the Giant Impact Hypothesis. It is suggests that the Moon should be 70% Theia in composition which should mean that there is greater variation in the geochemical values between Earth and Lunar rocks.

Recent research may have come across a solution to this problem. Scientists suggest that the Moon may comprise only 40% Theia and that Theia itself may have been similar to meteorites called enstatite chondrites, which have very similar compositions to the Earth. This would explain the similarity in Earth and Lunar samples in the case of a giant impact.

So the next time you look up into the night sky and see the moon shining majestically just remember the extraordinary manner of its birth. It is an amazing example of the beauty that can be born out of disaster and that even when you suspect the worst, not all is lost.

Further Reading:

http://bit.ly/1nEbeCq http://bit.ly/1zVsR6P

A Cool Infographic: http://bit.ly/19PGFef

Refrences:

http://bit.ly/1pViQXr http://bit.ly/1D0z1Y3

Image Credit:

Art – Dana Berry Source – Robin Canup, SWRI

A Magma Ocean

This is an artist’s impression of a molten planet, in this case an exoplanet close enough to a star to be heated by the strength of the tides. Even though this is a very different setup from our solar system, at one point 4.5 billion years ago the Earth looked disturbingly like this.

The early solar system was a violent place. Soon after the formation of the solar system, solid particles came together under the influence of gravity to form the building blocks of planets; chunks of rock we call planetesimals. Originally there were dozens, even hundreds of those objects, but as they orbited the sun, gravity stirred up their orbits and led them to collide.

Every collision between planetesimals released huge amounts of energy – the pull of gravity between two objects made them accelerate as they got close, and when they collided, the kinetic energy converted into thermal energy, massively heating the objects.

The formation of a planet the size of Earth or Venus would release huge amounts of energy, particularly during the final impact that led to the formation of Earth’s moon (http://tmblr.co/Zyv2Js1CMMD-S) The energy available in that sized impact is enough to heat the Earth so much that it would be hotter than the surface of the sun. Not all of the energy has to go into heating the planet, some can be expended by blasting material away, but it’s still an enormous amount of heat.

After the giant impact that formed the moon, Earth was covered by magma, maybe even a thousand kilometers deep. This magma ocean would have churned and radiated heat, eventually cooling enough that crystals started to form. Some crystals likely sank; others could have formed a crust at the surface.

This magma ocean left its imprint on the chemistry of Earth’s rocks today. The moon is nearly identical in composition to the Earth because it formed from debris sprayed out of the Earth during that final impact, but with a few important differences. Volatile components in the Earth, including things like noble gases, were lost to space, leaving the earth depleted in those elements. Other elements that dissolve in metals sank, eventually becoming part of Earth’s core - those elements are notably missing from the moon since they were locked into the core of the larger planet. These chemical similarities and differences were key in how scientists developed the “Giant impact” model for the moon’s formation.

The planet earth has healed from this impact, but this violent formation still left its chemical scars on the planet in ways we now know how to measure. 

-JBB

Image credit: http://bit.ly/1CFE7uX

Support a colleague?

If anyone was willing, a colleague of mine, who recently was awarded a US National Science Foundation fellowship to support her Ph.D. work in planetary science starting this fall just posted a GoFundMe page to support her and her mother this week. She literally just this week finished work on her masters thesis where she did isotopic analysis of a rock from Mars where the person running this page  did the initial survey of how that rock formed.  If you were interested or willing to read more, here’s the link:

http://gf.me/u/s2j7ku

I haven’t done this before despite the fact that this page is 5 years ol, so how about anyone who contributes via the TES blog end their contribution with 47 cents because that’s my favorite number due to Star Trek? Feel free to contribute $1.47 if you’re just willing to throw that to this page.

Thank you for your consideration.

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Let’s look at Venus – REALLY Close!

If the Moon were the Size of a Pixel…

Oh my gods! This post is not for the faint-hearted. If however you really want to go out and explore space, to boldly go where no one has gone before… be forewarned that the main foe on your journey will not be alien creatures, solar flares, or even stray asteroids. You will yearn for the company of a stray asteroid, believe me. Your mission statement will beto boldly overcome pure complete total boredom.

Josh Worth has created the universe’s most tedious tour of the solar system. It’s utterly brilliant. I dare you to take the trip from the Sun to Pluto at http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html Everything on this trip is to absolute scale (though some planetary positions have been approximated, since they are variable). The scale is lunar: that is, the moon’s size is reduced to a single pixel to establish the scale. Everything else on this epic journey is at the same scale – distances, sizes of planetary bodies, and the blackness and emptiness of space. Start there at the Sun, it’s quite huge on this scale, and you feel wow, this should be fun! then scroll through the solar system, scroll, scroll, scroll, and eventually you’ll get to… Mercury. Only the truly brave boldly scroll further…

I thought I had an understanding of how LARGE is space, and that it’s a pretty empty place. After all, I took astronomy and space physics. I watch all the Nova documentaries. But by the time I scrolled my way to the Earth, I was beginning to understand that the solar system is even LARGER than I’d estimated, and far more empty. I was beginning to comprehend the true scale of the size of space. The true insignificance of the dust mote we call the Earth. And this is the brilliance of this clip.

I don’t know if all computers scroll at the same rate, but mine is about 5 million km/second. That is, on this scale I’m surpassing the speed of light (299 792 458 m / s, or ~300,000 km/sec). Even this is not fast enough.

I tried; indeed I did. I considered it my scientific duty. Science is, after all, 99% tedium. But I did have to take a bathroom break somewhere around the asteroid belt, and somewhere past Neptune, someone in the house flicked on the microwave which caused the circuit breaker to trip, the computer to shut off, and… when I went back on, I found I cannot skip back to where I’d left my journey unexpectedly, but would have to start over again. Alas, I guess I am not made of the stern stuff needed to explore the universe.

Are you? How many of you can scroll scroll scroll all the way to Pluto? Annie R

With thanks to Josh for creating this tedious, boring, and utterly brilliant clip. PS – somewhere around Jupiter as I recall, he comments that were the Sun the proton of a hydrogen atom, then on this absolute scale it would take another five screens PAST the distance of Pluto to find its electron. Suddenly, not only is space huge and empty, but I’m feeling vastly vacant as well.