Mars was once a small, wet and blue world, but over the past 4 billion years, Mars dried up and became the red dust bowl we know today.
But how much water did Mars possess? According to research published in the journal Science, the Martian northern hemisphere was likely covered in an ocean, covering a region of the approximate area as Earth’s Atlantic Ocean, plunging, in some places, to 1.6 kilometers (1 mile) deep. More info
This stunning image shows the nebula cataloged as NGC 2359, but more commonly known as Thor’s Helmet. It does bear a striking resemblance to the headpiece worn by the Norse god, right down to the wings. The nebula, roughly 30 light-years across, is located about 15,000 light-years away in the constellation Canis Major.
Powering up this nebula is a Wolf-Rayet (WR) star known as HD 56925. WR stars are hot, massive giants late in their evolutionary cycles. This O-type giant, perhaps 20 times more massive than the Sun, has gone through a rapid loss of mass, casting most of its hydrogen out into space. The powerful stellar winds carrying this material outward shock the surrounding interstellar medium, causing it to glow. The wing structures were likely thrown off earlier by the progenitor star, while the central helmet portion of the nebula is a more recent bubble blown by the O-type blue giant.
The Thor’s Helmet nebula is not immortal. The central Wolf-Rayet star, having jettisoned most of its hydrogen outward, begins to fuse heavier elements, but that fusion process will end at iron. The outward pressure from fusion will cease, and the inward pressure of gravity will crush the star down, creating a supernova explosion. The nebula won’t survive the blast, but perhaps the resulting supernova remnant will take on an interesting shape of its own.