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Listening with trees

It’s not clear if enemy patrols spotted the man, an American soldier, climbing a tree in a remote part of France, hammer in one hand and large metal spike in the other. If they had there’s almost no chance they would have realised that the man was under the direction of the US Army's Chief Signal Officer and the tree was about to be transformed into a listening station to eavesdrop on German aircraft.

In the early days of radio, during the First World War, the Chief Signal Officer, Major General George Owen Squier was a pioneer in the use of trees as radio antennas. Trees, you see, were plentiful on the battlefield, and in Squier’s vision soldiers would one day be able to just hitch up a radio set to the nearest tree rather than lugging antennas around. Largely forgotten due to technological improvements which made radios more portable, Squier’s idea actually worked and not only that, still has relevance today in radio astronomy.

How this works is actually absurdly simple. Squier discovered one simply needed to hammer a spike into a tree at the right distance from the ground, and then connect it via a wire to a radio receiver. This turns the water in the trunk into an electrical conductor and works so well that Squier was able to use this to communicate via telegraphy with ships at sea, as well as listening in on communications between German aircraft and troops on the ground.

A 1919 article in Scientific American even speculated that trees would be great for amateur radio operators, who could not afford to erect large aerials. These possibilities obviously never came to anything, but research into the idea didn't stop there. Subsequent research found that it is also effective to wrap the tree in a copper coil. This has the advantage of allowing the receiver to be directional and tuned to particular frequencies. Work has also been done on using multiple trees together in a phased array, allowing even more precise control of the direction. In some cases trees can even outperform traditional antennas.

That brings us to astronomy. Some areas of radio astronomy, such as research into neutrinos,¹ require the use of large arrays of radio antennas, often erected in remote locations. It’s possible that by using tree-based antennas, astronomers could greatly reduce the costs of constructing and maintaining such arrays.

Recent research found that both types of tree antenna  – a simple wire or a coil wrapped around the tree – would be effective at detecting high energy neutrinos. They found that almost any type of forest would work, as long as they could space the antennas at the right distance from each other. Pine trees would work particularly well.

So far no one has built a tree-based array for astronomy, but the possibility is not as silly as it sounds.

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Solar System

• Samples returned by Chang'e 6 confirm existing models of the Moon’s history, showing that it was covered in a giant magma ocean after it formed. [Space.com]

• Dust devils on Mars have been found producing electricity, similar to lightning. First observed by the Perseverence rover, and then reproduced by scientists in a lab. [New Scientist]

• It’s not just Earth that experiences auroras. Using one of its spectrographs, JWST has observed auroras on Neptune. Unlike on Earth, the auroras are not at the poles because Neptune’s magnetic field is misaligned. [Space.com, NASA, EarthSky]

Galaxy

• Following the completion of its mission, Gaia has been put in a “retirement” orbit and powered down. [ESA, Space.com]

• New spectroscopic observations of a recurrent nova in the Large Magellanic Cloud found the signature of extremely energised silicon, suggesting much more energy than expected. Just as surprising, there was no sign of other elements that should be there. [Space.com]

• JWST has managed to snap photos of exoplanets orbiting a start 130 light years away. We already knew the planets were there, but this is the first time we’ve been able to see them. [Sky at Night]

• New observations from the ALMA radio telescope array have found violent fillaments moving gas and dust in the galactic centre. [Space.com, Universe Today]

Universe

• ALMA has found oxygen in the youngest known galaxy! That suggests, a mere 300 million years after the Big Bang, the earliest generation of stars had already lived and died, making and releasing new elements in the process. [Space.com, ESO, Universe Today]

• The first results from the European Space Agency’s Euclid mission have been published, and it’s an absolute goldmine of galaxies. [The Guardian, Space.com, National Geographic]

• The LIGO gravitational wave detector has recorded several mergers of intermediate-mass black holes (IMBHs) – ones which are bigger than stellar-mass black holes and presumably form through mergers of smaller black holes. Surprisingly, LIGO has found that IMBHs exist in a range of masses previously thought to be impossible. [Universe Today]

• Hubble has observed the Large Magellanic Cloud’s gaseous halo and found that it is much smaller than expected, 10 times smaller than those of similar galaxies. This is a result of the LMC’s close encounter with the Milky Way. [ESA]

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Finally

Some of the best discoveries were made entirely by accident. Those new moons found orbiting Saturn the other week? A bunch of them were found because someone accidentally took some long-exposures of Saturn (five minutes is long for something as bright as Saturn):

What is Three Alpha? Other than being the name of the newsletter you’re reading now, the name “three alpha” comes from the triple-alpha process, a nuclear chain reaction in stars which turns helium into carbon. Read more here.

Who writes this? My name is Dr. Adam McMaster. I’m an astronomer in the UK, where I mainly work on finding black holes. You can find me on BlueSky, @adammc.space.

Let me know what you think! You can send comments and feedback by hitting reply or by emailing [email protected].

1  There are several kinds of neutrino detectors. The most famous ones are underground and use large volumes of purified water, but air-based detectors are a potentially important way to detect neutrinos at different energy levels.