UFO'S of UAP'S, ASTRONOMIE, RUIMTEVAART, ARCHEOLOGIE, OUDHEIDKUNDE, SF-SNUFJES EN ANDERE ESOTERISCHE WETENSCHAPPEN

What's an Earth-Like Planet Anyway? — **Artist's rendering of the Kepler Space Telescope.**
**Credit: NASA/JPL-Caltech/Wendy Stenzel**

Project Blue contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

For centuries, humans have wondered whether Earth is unique in the universe, or if similar planets exist out there. Even a decade ago, we still did not know — but then NASA's Kepler Space Telescope made discoveries that changed everything.

Thanks to that important mission, the answer became clear: other planets like ours are out in the cosmos. We just haven't seen one with our own eyes yet.

Since its 2009 launch, Kepler has discovered more than 2,000 confirmed exoplanets and has given us a huge amount of information about their orbits and sizes. The planets found range greatly in their masses, composition and orbital distances: for instance, enormous gas giants orbiting incredibly close to their stars, called hot Jupiters; planets that orbit two stars, called circumbinary planets; and rocky planets with the potential to be like Earth. [In Mission To Find Another Earth, Project Blue Hopes To Inspire (Video)]

The planets considered Earth-like are rocky on their surface and about 0.5 to 1.5 times the size of Earth. They also land in the "habitable zone" of their orbiting stars, meaning they fall in the sweet spot of orbital distance — not too close and not too far away — and therefore have the potential to be able to support liquid water on their surfaces. The ability to support water is huge, as it means the planet could have the potential to support life.

Kepler showed us these planets are common in the universe. In fact, we now know there are more potentially habitable planets in our galaxy alone than there are people alive on Earth. One out of every two sun-like stars you see in the night sky has a rocky, Earth-like planet in its habitable zone.

**Depiction of NASA's Kepler mission's smallest habitable zone planet: Kepler-62f.**
**Credit: NASA Ames/JPL-Caltech/Tim Pyle**

Earlier this year, one potentially habitable planet made news when scientists discovered it orbiting the nearby red dwarf star Proxima Centauri. That planet, called Proxima b, which has similarities to Earth that include orbiting in the habitable zone of its star, so the potential to support water, and a size about 1.3 times that of Earth.

**Artist's conception of the surface of Proxima Centauri b (Proxima b, for short).**
**Credit: ESO/M. Kornmesser**

We now know these planets exist, but we have yet to see them. To know more about a planet's Earth-like properties, such as whether it hosts water or oxygen, further specific detection methods are needed. Thanks to recent breakthroughs, the technology now exists to capture a direct image of an Earth-like planet outside our solar system. That's what we aim to do at Project Blue.

Our mission is to capture an image, visible to the human eye, of one of these worlds. Proxima b is an unlikely candidate, as it orbits so close to its small, dim star that it would be extremely difficult to image with a telescope. Project Blue is therefore targeting our best chance at success: our stellar neighbor Alpha Centauri.

Our goal is to see a "pale blue dot" that could indicate the presence of oceans or an atmosphere — and the potential to support life. Since Alpha Centauri is a binary system, it doubles our chances, and the probability that we'll find at least one potentially habitable planet is around 85 percent.

Capturing the first image of a planet like ours and seeing it with our eyes will help us begin to characterize its properties and spark a movement to quickly further research. The photograph of Earth 2.0 would be a defining moment in human history and is sure to transform how we see ourselves in the universe.

Project Blue is running a crowdfunding campaign right now to fund initial research and design.

Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

How to Build a Death Star — **The moon-size, weaponized space station, Death Star, is seen in "Rogue One: A Star Wars Story."**
**Credit: copyright 2016 Lucasfilm Ltd. All Rights Reserved.**

This article was originally published at The Conversation. The publication contributed the article to Live Science's Expert Voices: Op-Ed & Insights.

I'm very excited about seeing Rogue One: A Star Wars Story, which tells the tale summarized in the original Star Wars' opening crawl. This is the story of how the rebels stole the plans to the original "Death Star" – a space station the size of a small moon with a weapon powerful enough to destroy a planet.

If we could get our hands on those plans, could we build a similar fortress? I decided to try to work out some aspects of how a Death Star might actually work. In Star Wars lore, the 120 km (75-mile) diameter space station was made from quadanium steel (a fictional metal alloy) and crewed by 2m Imperial personnel, including officers, Stormtroopers and TIE pilots.

So would it possible in the real world? Let's not worry about the vast quantities of raw materials required. For example, at current production rates of steel it would take 182 times the current age of the universe to accrue enough. I'm more concerned conceptually with how to power such a colossal battle station and how to generate gravity for everyone on board. It turns out our conventional technologies might not cut it.

The International Space Station requires about 0.75 W of power for every m³ of the space station. These are provided by eight solar arrays, 112 feet (34m) long by 39 feet (12m) wide. Even if we had 100% efficient solar panels covering the much larger Death Star, we'd still be a factor of 45 times short of the ISS's power requirements per unit volume. Not to mention that power would severely diminish if we took the space station further away from the sun.

You might think we could learn lessons from the sci-fi classic 2001 A Space Odyssey in terms of the gravity and just spin the Death Star to create artificial gravity via centrifugal forces. To replicate the gravity on Earth (9.81 metres per second squared or 1 g), the station would only need to revolve once every 3.5 minutes, which doesn't sound too absurd.

But there was a reason the station was ring-shaped in 2001. The centrifugal force is proportional to the radius of your circular path. As you travel either towards the centre of the station or towards the poles, this radius decreases meaning the artificial gravity would start to vanish. If indeed gravity was created this way, it calls into question the Death Star's spherical design.

Dyson sphere

Perhaps the clue was in the name the whole time. What if at the heart of the Death Star is an artificial star? Surely that would solve the gravity problem? This makes the station something of a Dyson sphere, the sort of technological megastructure physicist Freeman Dyson imagined advanced civilisations might be able to build to harness all the energy from their stars. However, Dyson spheres of the rigid shell variety usually run into problems from being under immense stresses due to the gravitational forces. Even if the sphere isn't ripped apart by this, just a small push certainly would be enough to send the structure crashing into its star.

But Dyson spheres are usually imagined to be the size of the Earth's orbit around the sun. For a much smaller Death Star, most of the problems with the Dyson sphere go away. The 13.2 km diameter reactor core would only require a mass 370 times less than our moon's. It turns out while steel and titanium would just about fail under these conditions, the wonder material graphene, for example, could easily withstand the gravitational forces involved.

And we wouldn't actually need a real star at the centre of the station – the future technology of nuclear fusion could easily provide enough power. While at the moment we tend to put more energy in than we get out in our fusion experiments, many plasma physicists think the key is going bigger and hope that the ITER experiment, which will be one-third of the volume of an Olympic swimming pool, will turn the tide in this regard. If successful, we could expect power from our Death Star up to two million times that consumed by the entire human race.

But there are still problems. The pressures involved inside our Death Star reactor would be immense. The artificial star's own gravity would not be enough to contain the fusion plasma, so we would need something extra. As we've learned from thinking about lightsabers, magnetic fields could provide the solution. The only snag is that we'd need some of the strongest magnetic fields in the universe – a million times greater than we've ever created on Earth and comparable to those of magnetars – a type of neutron star with an extremely powerful magnetic field.

Back to the drawing board it seems, unless I can get my hands on those plans …

Martin Archer, Space Plasma Physicist, Queen Mary University of London

This article was originally published on The Conversation. Read the original article.