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If a planet receives only 7.5 hours of daylight in its 30 hours cycle, how will be the conditions on it?

The considerations are that the planet receives as much sunlight as Earth, and is in the Goldilock zone of the star's system. The reason the planet receives less sunlight is because there is another planetary body in front of this planet which casts a shadow on this planet.

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    $\begingroup$ It will have shorter days $\endgroup$ – Helmar Jan 10 '17 at 10:52
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    $\begingroup$ How can the obscuring body stand still in the same relative position with respect to the planet and its sun? I am afraid the best you can get is very frequent eclipses. $\endgroup$ – L.Dutch - Reinstate Monica Jan 10 '17 at 11:13
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    $\begingroup$ This is not physically possible. $\endgroup$ – gerrit Jan 10 '17 at 11:25
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    $\begingroup$ I'm afraid your planet is really a moon $\endgroup$ – SilverCookies Jan 10 '17 at 12:10
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    $\begingroup$ Welcome to Worldbuilding, AniruddhaKhanwelkar, you have posed an ingenious question. Can you clarify the arrangement of the two bodies, I assume there are two planets moving together in almost the same orbit. Is this so? The shadow must fall on your planet during late morning to early afternoon. As if there was a permanent eclipse every day. Am I right? This means there will be two short periods of daylight adding up to 7.5 hours or 25% of a complete rotation. Please let me know if this is wrong. $\endgroup$ – a4android Jan 10 '17 at 12:28
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Due to the shorter daylight time lapse the vegetation will probably find a better way of feeding than photosynthesis, reducing the green on the landscapes and turning it into more reddish/purple tones. Plants and trees would adapt to the colder conditions with cactus-like shapes rather than typical plants. The few sun hours would also cause them to be taller than we would expect here to reach sunlight.

Also expect the general weather conditions worse than on Earth due to the sudden exposition to heat after long, dark and cold nights.

The lifeforms, well, take a look at any Ice Age film to get an idea of how they'd evolve, even tho I'd expect mammals to be the only ones to live in such conditions since they can generate their own heat.

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  • $\begingroup$ I agree with bits of this, although not all of it. For example you could equally argue that you would have large broad-leafed plants to gather as much light as possible. Equally endothermic animals are a lot less energy efficient, so you might have exothermic ones that just hibernate through the night then revive when the sun rises. $\endgroup$ – Tim B Jan 11 '17 at 13:31
  • $\begingroup$ @tiimb yes I do agree with you there are so many variables on this subject plus once we really start exploring other planets were be able to know the real answer to this $\endgroup$ – Sandy Jan 12 '17 at 8:58
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Alien life could exist on planets without stars, thriving on hydrothermal vents below a thick layer of ice on their cold dark surfaces, an astrophysicist has said.

Sean Raymond, from the Laboratoire d'Astrophysique de Bordeaux in France, has said that under certain conditions, life on these rogue planets could even host a global biosphere.

Writing for Aeon magazine, Raymond said there are potentially tens of billions of free-floating Earth-sized rocky worlds in the Milky Way that have no sun to provide them with energy.

"To have any chance of life – at least life like our own – a free-floating Earth would need liquid water. And to have liquid water, a planet needs to keep warm. But space is ridiculously cold, just a few degrees above absolute zero. How could a rogue planet stay warm with no Sun?" he wrote.

He said that all planets generated heat from their interiors, with internal heat from the giant collisions that formed them trapped there. This heat bubbles up slowly to the surface and lasts for billions of years – but provides only a tiny amount of energy in comparison to a star's heat.

To keep in the heat, a planet would have to have a layer of ice at least 10km thick, while a thick atmosphere would also help – hydrogen would be the best atmospheric gas for the task.

"A free-floating Earth with a thick hydrogen atmosphere could keep its surface temperature above the freezing point of water. The planet could have lakes and oceans [and possibly life] on its surface. But its atmosphere would need to be at least 10 to 100 times thicker than Earth's."

What would life be like?

Unlike organisms on Earth's surface, there are lifeforms that do not need the Sun to survive. "They are called chemoautotrophs and they live on the ocean floor," Raymond wrote. "They make their own organic carbon using energy leaking out from inside the Earth. These organisms form the basis of the thriving ecosystems found around deep-sea hydrothermal vents."

America from space Earth may not be the only life-supporting planet in the universe. In fact, planets without a star in their system could also support lifeNasa Earth Observatory Chemoautotrophs rely only on pre-existing conditions provided by the likes of hydrothermal vents to survive. If a free-floating planet were to have life, it would have to be in the form of chemoautotrophs.

As we do not know how life began on Earth, there are a number of theories as to how life on a planet without a star could be seeded in the first place, one being the "deep sea vent hypothesis", which says hydrothermal vents acted as a cradle for early life. "And rogue planets are likely to be littered with hydrothermal vents," he said.

On Earth, hydrothermal vents contain an array of plants and creatures, including tube worms, scaly-foot snails and eyeless shrimps and the producers of these ecosystems are the chemoautotrophs.

"A free-floating planet could be speckled with biospheres, each clustered around a local heat source. They might even host giant plants such as tube worms. Each oasis would start off isolated and probably host its own unique species, but on some rogue planets these ecosystems could merge into a global biosphere."

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You asked "how will be the conditions on it?", and not how LIFE would exist on in, so here is my answer;

My first interpretation of "that the planet receives as much sunlight as Earth" is that; due to its position from whatever star type it orbits, that the planet would receive the same amount of solar flux as earth, were it not for the secondary planet, in which case 7.5 hours of actual sunlight would result in Artic conditions on the surface of the planet.

My second interpretation of "that the planet receives as much sunlight as Earth" is that; due to its position from whatever star type it orbits and accounting for the 22.5 hours of darkness, the planet's surface receives the same flux of solar energy that the earth does, making it about as temperate as earth, just darker. This would be more comparable to caves that have limited access to light, which are found across our own earth from pole to pole, but here those conditions would be on the surface and in both cases only depend on where you are on the planet.

I make the assumption for the second planet that blocks the sun for the other 22.5 hours that it will have to be a satellite (moon) or binary twin of the primary planet in order for the solar eclipse to occur at all so often and for so long. Reason: A reasonably sized inner planet on an orbit close enough to the sun to orbit fast enough to be in between the two so often would be too far from the planet to cause a total eclipse. From that, there will be tidal forces much greater than we experience from our own moon and would cause a lot of geological activity. If there are oceans they'd be very tumultuous and volcanic activity would also be very common.

An increased volcanic activity could increase or decrease the greenhouse effect that the planet experiences. Depending on the volcanic gases they could block more sunlight from reaching the surface making it even colder. If the gases allow light to the surface but then reflect any radiation that was reflected up, back down, then you would get a warmer planet.

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