The Earth Story

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

A kipuka on the Moon

Kipuka is a Hawaiian term for a common occurrence on the slopes of the active volcanoes. Trees grow all over the island of Hawaii, including on the active parts of the volcano. In those areas, those trees will occasionally be overrun by streams of lava which burn away the vegetation where it flows. But, the lava doesn’t cover the entire area; it moves in channels and flows downhill to the ocean. Consequently, eruptions commonly leave behind a lush oasis of vegetation surrounded on all sides by barren lava flows called a kipuka.

There aren’t trees on the Moon, but there is topography. Craters and volcanic flows create high ground around which lava can flow.

This image shows a lunar kipuka; an area of the land surrounded by younger lava. The large crater in this photo has been breached at its left-hand side by lavas from Mare Imbrium, one of the large lava fields on the Moon’s near-side.

There is even a shoreline preserved in this crater, best-expressed on the inside of the crater at the right-hand side of the image as a line parallel to the crater rim.

This image was taken by the LROC instrument, the high-resolution camera on the Lunar Reconnaissance Orbiter mission. The crater itself is ~2.7 kilometers wide and was originally about 500 meters deep; much of that depth has been filled in by the lava flow.

-JBB

Image credit: NASA/GSFC/Arizona State University http://lroc.sese.asu.edu/news/index.php?%2Farchives%2F787-Lunar-Kipuka.html

Lunar and Planetary Science Conference 2016

Head over to our twitter feed - the scientist who runs this blog is currently at the 2016 Lunar and Planetary Science Conference (presenting research about Mars on Wednesday). I’ll be live tweeting the conference, including stuff on what the experience of a scientific conference is like, and a lot of the science results. 

Other LPSC Microbloggers Also follow the Hashtag #LPSC2016

NASA has released a spectacular animation presenting a unique view of the moon as it was photographed last month passing between the sunlit side of Earth and a satellite positioned 1.6 million km away.

Taken by a camera on the Deep Space Climate Observatory (DSCOVR) satellite between 3.50pm and 8.45pm EDT on July 16th, the images show the fully illuminated ‘dark side’ of the moon that is not observable from Earth.

The images were taken by the US space agency’s Earth Polychromatic Imaging Camera (Epic), a four megapixel CCD camera and telescope on the DSCOVR satellite.

Epic maintains a continuous view of the fully illuminated Earth as it rotates, providing day-to-day scientific reports of ozone, vegetation, cloud height, and airborne aerosols.

From next month, the camera will provide a series of Earth images allowing study of daily variations over the entire globe and NASA will post daily colour images to a dedicated public website; the images will show different views of the planet as it rotates through the day and will be accessible 12 to 36 hours after they are obtained.

About twice a year the camera will capture images of the moon and Earth together as the orbit of DSCOVR crosses the orbital plane of the moon.

-Jean

Check out the animation here: http://tmblr.co/Zyv2Js1rLG6B9 http://www.nasa.gov/feature/goddard/from-a-million-miles-away-nasa-camera-shows-moon-crossing-face-of-earth

The minerals of the Moon

Studying the rocks collected on different lunar missions has revealed a number of surprising results, as well as a great deal of information about the composition of both our planet’s satellite – and the Earth itself.

Although researchers had a good idea of what Moon rocks would be like, the materials brought back to laboratories on Earth contained some surprises. They were initially classified into four large groups: crystalline igneous rocks like basalt; crystalline igneous rocks, such as gabbros; breccias and microbreccias; and sands and soils. In this way more than thirty species of minerals in Moon rocks and four more in the remains of meteorites were identified.

Following the initial studies it was found that the most abundant minerals in all kinds of rock were pyroxenes, feldspars and ilmenite, a relatively rare oxide on Earth. However, although most of the species identified are more or less generally common in terrestrial rocks, some were rare and a few were first discovered in Moon rocks.

The lunar maria, or seas, cover 16% of the surface and are of volcanic origin. Volcanoes were very active in the past although they no longer erupt today. The first crewed mission to the Moon, Apollo XI, landed in the sea of Tranquillity and collected samples of basalts, the predominant rock in lunar maria, as was confirmed by later missions. The basalts in the lunar maria contained titanium dioxide in varying concentrations.

Ilmenite is an oxide of titanium and iron that is relatively rare on Earth. However, it is the most abundant mineral on the Moon—between 10 and 18% of many rocks by weight. It is also the mineral with the largest crystals, with some being several millimetres long. Lunar ilmenite is very pure and many examples have an unusual high titanium content. Other common lunar oxides are chromite, spinel, rutile, baddeleyite, as well as some silica minerals: quartz, cristobalite and tridymite.

The lunar highlands cover the majority of the Moon’s surface and are coated with regolith, a layer of grey rock dust produced by countless meteorite impacts. Other kinds of rock predominate in this region, for example anorthosite consisting of plagioclases, olivines and pyroxenes; norite, a rock similar to gabbro but containing orthopyroxene; and troctolite, a rock consisting solely of anorthite-type calcic plagioclase and of olivine.

Apart from oxides and silicates, the most abundant basic components of lunar rocks, other unexpected minerals have also been identified. For example apatite and withlockite, both calcium phosphates, and aragonite, a carbonate, are just a few of the surprising substances found in samples. Native elements such as copper, tin and iron, were also found, together with sulphides such as troilite and pentlandite.

The astronaut Neil Armstrong, one of the crew members of the first mission, has had a mineral, armstrongite, dedicated to him. It is a hydrated cyclosilicate of calcium and zirconium with a momoclinic structure. However, armstrongite was not found in lunar rocks but was discovered in terrestrial granitic pegmatites.

~ JM

Image Credit: NASA/JPL sourced from http://1.usa.gov/1f8gpP5 on 03/07/15

More Info: NASA: http://1.usa.gov/1H4uOox Lunar Surface: http://bit.ly/1T9PfWA Moon packed with precious titanium: http://bit.ly/1NBH6X8 Wu, Y., Zhang, X., Yan, B., Gan, F., Tang, Z., Xu, A., ... & Zou, Y. (2010). Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data. Science China Physics, Mechanics and Astronomy, 53(12), 2160-2171 http://webmineral.com/

One day the Earth might copy its gas-giant brothers 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

Want to play with Craters on the Moon? Moon Zoo will let you.

Moon Zoo is a website that is all about the Moon, so you fans of our closest neighbour should definitely give it a look. It is a facility to study the lunar surface in unprecedented detail and to help visually classify millions of images taken by NASA’s Lunar Reconnaissance Orbiter (LRO). It has been running for a few years now but I don’t believe all too many people are aware of it.

There is a Crater Survey in which you’ll be shown a randomly selected LRO image of the lunar surface. Your task is to identify any craters that you can see in the image by moving the cursor to a crater and then clicking on the ‘Crater’ button.

How craters appear will depend on whether it was morning, midday or evening – the shadows will change dramatically over the course of the day. Once you’ve marked all the craters, you can click on the ellipse (cursor) to stretch and move them so they mark the right size crater. Then you will study each crater for signs of boulders in or around them and for anything ‘odd’ about each crater.

If that’s not cool enough, there is “Boulder Wars” in which you are asked to compare two LRO images of the lunar surface and decide which of the two has the most boulders, and if there’s anything of interest in either image.

These tasks could provide hours of enjoyment if you have a keen eye for detail and it’s your kind of pastime and who knows, you might just discover something significant or unique on our Moon. If not, it’s the closest way of seeing such awesomeness up close

To take part, or just to take a look, start off at http://www.moonzoo.org/how_to_take_part

Enjoy!

~ JM

Photo Credit: http://www.moonzoo.org/

TRANQUILLITYITE, A LUNAR MINERAL, FOUND IN WESTERN AUSTRALIA During the days of the Apollo moon programme, hundreds of kilograms of rock samples were taken back to Earth by astronauts. Geologists studied these samples extensively and determined there were 3 minerals unique to the moon: armalcolite, pyroxferroite and tranquillityite. Tranquillityite was found in mare basalts collected during the Apollo 11 lunar mission to the Sea of Tranquillity in July 1969 (the mineral is named after the Sea of Tranquillity). Armalcolite and pyroxferroite have since been found on Earth’s surface but tranquillityite was only ever found in meteorite samples. That is, until now. Birger Rasmussen, a palaeontologist at Curtin University in Perth led a team that has found natural samples of tranquillityite in several sites in Western Australia. The mineral has been found in six dolerite dikes and sills, in amounts so small that they are the width of a human hair and just 150 micrometres in length. Tranquillityite is comparatively delicate and tends to easily break down when exposed to normal surface climatic events (like heat, rain and wind). It develops during the late stages of crystallisation of molten rocks in oxygen-poor conditions. The team had come across some interesting rocks that resembled the lunar rocks they had previously been studying. They subjected the sample to a blast of electrons; the trajectories of the blast are unique to each mineral. They found a perfect match to the lunar samples. Tranquillityite [Fe2+8(ZrY)2Ti3Si3O24] is mostly made up of Si, Zr, Ti, and Fe, with minor Al, Mg, Mn, Ca, Nb, Hf, Y, and rare earth elements (REE). Before you get excited about mining prospects, know that it doesn’t seem to have much economical value. Using Uranium–lead (U–Pb) dating on tranquillityite from sills intruding the Eel Creek Formation, northeastern Pilbara Craton, gave a 207Pb/206Pb age of 1064 ± 14 Ma (1.064 billion years old). The mineral can give researchers insights into the age of other rocks in which it is found. -TEL http://phys.org/news/2012-01-lunar-mineral-tranquillityite-western.html; http://news.sciencemag.org/sciencenow/2012/01/rare-moon-mineral-found-on-earth.html; Tranquillityite: The last lunar mineral comes down to Earth, Geology, v. 40 no. 1 p. 83-86. First published online November 23, 2011, doi: 10.1130/G32525.1 Image Credit: Birger Rasmussen