Both Mars and Venus have been objects of scientific
and popular speculation since at least the beginning
of the 20th century, and since the 1960s spacefaring
nations have been sending robotic probes to explore
these two planets. (22)----, Mars has drawn far more
attention. Since 2002 no fewer than two Mars probes
have been actively gathering data during any given
year. There were actually seven used in 2015 alone.
This is (23)---- because Mars is far more hospitable than
Venus, where surface temperatures can reach 480 °C,
surface pressure is 92 times that of the Earth and the
planet is permanently surrounded by thick clouds of
sulfuric acid. We have direct evidence that water once
flowed and pooled (24)---- Mars. So, it can be assumed
that life once existed there and (25)---- at present. Venus
is far more Earth-like than Mars in its size, composition
and surface gravity, but (26)---- its harsh environment, it
could never host life