by passing satellites past it we can calculate its weight and look at light spectrums from the planet. Mars is 0.15 times earths volume but 0.1 times earths mass, the same could be applied to this 10 times bigger planet. Its all astrophysics.
Second question; life wouldn't change, as we move at the same speed as the planet we are on you wouldn't notice.
You would live longer than people on earth because of time dilation. In space the faster the go or the heavier a planet the more time is stretched, So while we would feel like we lived a hundred years people on earth would have seen us live 105 years
Time dilation - Wikipedia, the free encyclopedia
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