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Olivia: This week we’re soaring above and diving below the ocean’s surface, to take a look at solar engineering feats and new research on cancer in shellfish. I’m Olivia Gordon, and this is SciShow News.

Flying across the Atlantic isn’t much of a big deal these days – in fact, over 2,000 transatlantic flights are made every day. But last week, people around the world celebrated one aircraft’s successful journey from New York City to Seville, Spain. This plane, called Solar Impulse 2, completed the first transatlantic flight powered only by the sun. This was the 15th leg of the plane’s trip around the world, and the solo pilot, Bertrand Piccard, was in the air for 71 hours and 8 minutes. The project hopes to raise awareness of solar technology, and inspire more people to adopt energy solutions that save natural resources.

Solar Impulse 2 has different engineering constraints than your regular fuel-burning aircraft. Over 17,000 solar panels made of thin slices from a single crystal of silicon – also known as monocrystalline photovoltaic cells – cover the body, tail, and wings of the plane. When sunlight hits these solar panels, the electrons on the silicon atoms are knocked off and move around, which generates an electric current and keeps the motors running.

Because this plane is completely powered by the sun, the engineers wanted to maximize its size to fit more solar panels. But they needed to keep it as light as possible to best use the power the panels provide. As a result, Solar Impulse 2’s 72-meter wingspan makes it wider than a Boeing 747 airliner but the mass is only that of a large car! And with long flights that can last multiple days, there’s also night to worry about.

So how do you fly by the energy of the Sun when there’s no sunlight? Batteries! Four energy-efficient batteries are tucked under the wings, behind the propellers. They get charged up during the day by the the solar cells and tapped into at night. The co-founders of the Solar Impulse project – Bertrand Piccard and André Borschberg – are taking turns flying this plane in its round-the-world tour.

It’s broken lots of records, but had a few setbacks too. Like, after an epic 117-hour flight over the Pacific Ocean last summer, the batteries were damaged from overheating in the tropical climates. The aircraft was grounded until Spring 2016, when the engineering team developed better heating and cooling systems and repaired the batteries.

Onward from Spain, Solar Impulse 2 has just one more planned stopover before landing in Abu Dhabi hopefully later this month, where its world tour started. The next leg should be taking off soon, depending on the weather, and you can track the plane’s progress live online.

There are still lots of engineering challenges to solve before solar transport becomes common, like the price, mass, and efficiency of photovoltaic cells. But the Solar Impulse project has shown it is possible to cross oceans and travel around the world, just using the power of the sun.

Let’s switch from flying over the sea to studying the creatures beneath it, because contagious cancers have been discovered in shellfish. Cancers are basically mutated cells that start to replicate and spread out of control. The damage they cause can be devastating in our own bodies, but they’re almost impossible to pass between people because the foreign cells would trigger an immune system response. We’ve talked about a few special exceptions before, in tasmanian devils, dogs, and soft-shell clams. But the findings from this new research paper published in Nature last week doubles the number of examples we know about.

The researchers at Columbia University Medical Center were studying shellfish known as bivalves – mussels, cockles, and clams. Many bivalve species get this cancer called disseminated neoplasia [neo-play-zhuh], where large, abnormal cells clog up their circulatory systems. We discovered the disease in the 1960s, but nobody really knew what caused it. So researchers started studying the DNA of these strange cells and surrounding healthy tissue. Let’s start with the mussels.

The cancerous cells were definitely from a mussel – not a bacteria, virus, or parasite infection – but they didn’t match the genetics of any of the host mussels. Instead, the abnormal cells were very similar to each other, like they started in one and hopped from mussel to mussel – spreading like an infectious disease! They found the same thing in cockles, but this time there were two different tumor clones being passed around. And the cancerous cells found in golden carpet shell clams didn’t even belong to that species – they came from its neighbor, the pullet shell clam! But what’s strange is the pullet shell clams don’t normally suffer from disseminated neoplasia. So one theory is that this cancer somehow switched over to golden carpets before the pullet shell clams developed resistance – and it lives on in this new species.

Which would be remarkable: cancer spreading between individuals and across species. There’s still so many questions, though: Are these cancers old or new diseases? Also, why are these spreading cancers so common in shellfish? Have we just not spotted them in other species? We’re learning so much about different cancers all the time, but this complex disease is still bringing new surprises.

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