Sky & Telescope - January 2021 - 11

NASA GODDARD

signal could be ampliﬁed. Moreover, insitu instruments could identify multiple
wavelengths at which the molecule
absorbs light.
There are several proposals for missions to Venus, but not all of them
would be able to detect phosphine. Two
of NASA's four Discovery Program ﬁnalists, DAVINCI+ and VERITAS, would
send missions to Venus as early as 2026.
VERITAS would carry instruments with
high spatial resolution but moderate
spectral resolution - probably not good
enough to see phosphine.
DAVINCI+, on the other hand, would
carry an entry probe that would measure the atmosphere's composition as it
ﬂoats down to the surface. The tunable
laser spectrometer the probe will carry
could in theory detect phosphine.
The European Space Agency's EnVision orbiter, proposed for launch in the
early 2030s, would have a mass spectrometer in its payload, but it's unlikely
that it would be able to detect the gas.
In addition, NASA's Venus Flagship
Mission Study has proposed a combined
orbiter-balloon-lander mission, which
could launch in the 2030s if approved.
"The balloon will explore the cloud
layer for two months, with speciﬁc
instruments designed to detect biological material if present," says Colin
Wilson (Oxford).
A spacecraft could arrive at Venus
even sooner with a private venture:
Rocket Lab, an aerospace manufacturer
and smallsat launch service provider,
has announced that it is planning a
Venus mission that could ﬂy by 2023.
While future exploration will provide
more deﬁnitive evidence, legacy data
from NASA's Pioneer Venus mission,
which launched in 1978, appear to support phosphine's presence.
That mission's entry probe carried a
neutral mass spectrometer, which analyzes gases in situ to suss out their elemental composition. In a new analysis
of the 42-year-old data, Rakesh Mogul
(Cal Poly Pomona) and colleagues ﬁnd
evidence of phosphine, as well as other
molecules such as methane and ammonia. The study was posted on the arXiv
astronomy preprint server.

IN BRIEF
More Underground Lakes
on Mars

S Artist's concept of the DAVINCI+ mission's
probe descending through Venus's atmosphere

TIME WILL TELL
As for whether the phosphine on Venus
is really a biosignature, that remains to
be seen. For starters, even in the relatively cool cloud decks, life would still
have to endure an environment that's
around 90% sulfuric acid.
"My gut tells me an unknown photochemical process is going on," says team
member William Bains (MIT). "I think
the chances of there being life on Venus
are very small."
Indeed, chemistry labs across the
globe are already investigating possible
inorganic production routes, to see if
anything besides life could account
for the molecule's presence in Venus's
atmosphere.
Sousa-Silva is similarly cautious. "My
science tells me the detection is true,
but it's pretty wild," she says. "I hope
that everyone will get their models running and try and ﬁnd alternatives that
explain this."
"I have reached the limits of my
knowledge," she adds, "and I welcome
the rest of the scientiﬁc community to
join in the fun."

New analysis of data from the European
Space Agency's Mars Express orbiter
strengthens the case for super-salty
lakes under Mars's south polar cap, first
discovered in 2018 (S&T: Nov. 2018, p.
8). Sebastian Lauro (Roma Tre University,
Italy) and colleagues reported the result
September 28th in Nature Astronomy. Using a new analysis technique on 134 radar
images taken over 10 years, the researchers not only confirmed the probable presence of an underground lake, they found
that it has friends: The "large body of
water [is] encircled by patchy water pools
or wet areas of smaller extent," they write.
The largest putative lake is about 20 by
30 kilometers (12 by 19 miles); the smaller
patches appear as 5- to 15-kilometer-wide
spots. The nature of the lakes remains a
matter of speculation: To maintain liquids
in a place where temperatures might
reach as low as 150K (-120°C or -190°F),
the water would have to be a hypersaline
brine. Other researchers argue in favor of
an additional heat source such as volcanism. Regardless of how liquids exist, the
evidence for sub-ice liquid-water ponds
has grown strong.
■ EMILY LAKDAWALLA

Sky & Telescope - January 2021

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