76 Science & technology The EconomistFebruary 22nd 2020
21launch, in 2021, of the James Webb Space
Telescope and the opening of new observa-
tories on the ground, such as the Extremely
Large Telescope (elt) in Chile. These will be
able to repeat, for some nearby exoplanets,
the first of Sagan’s experiments with Gali-
leo—the search for biosignatures. But, even
if they find them, exciting as that would be,
it would say nothing about the crucial final
letter in seti, the “I” for intelligence.
The search for intelligence was boosted
in 2015 with the launch of Breakthrough
Listen, a project paid for by Yuri Milner, a
software billionaire with a background in
physics. This enterprise, on which Dr Sie-
mion is chief scientist, is planned to last
ten years and expected to cost $100m. It is
intended to survey the 1m nearest stars in
detail, scan the entire plane of Earth’s
home galaxy, the Milky Way, and also listen
for messages from the 100 closest galaxies.
It is paying for astronomers interested in
setito have time on more than a dozen big
radio observatories around the world, and
it collects in a day an amount of data that
used previously to take a year to gather.Hello?
Nor is Breakthrough Listen alone. On Feb-
ruary 13th the setiInstitute, a not-for-pro-
fit organisation in California, and Ameri-
ca’s National Radio Astronomy
Observatory, announced a collaboration.
The observatory operates the Very Large Ar-
ray (vla), a radio telescope in New Mexico
that features in the film “Contact”. The col-
laboration allows setiresearchers to tap
the entire stream of data the vlarecords as
it carries out its routine experiments.
The partnership will become even more
useful for setiresearchers if the vlagets a
proposed upgrade that would greatly en-
hance its sensitivity. This next-generation
instrument would be good enough to de-
tect electromagnetic radiation leaking
from planets, similar to the television and
radio channels that Sagan measured leak-
ing from Earth.
Nor, despite the importance of radio
waves, will future setisearches stick to
that part of the spectrum. Alien civilisa-
tions might, for example, use laser flashes
as optical beacons to signal their presence.
If a nanosecond-long pulse of such light
were pointed in the direction of Earth, it
could be made energetic enough to seem
brighter to human instruments than any of
the stars in the same part of the sky.
Moreover, as observatories get better,
astronomers will also be able to spot small,
potentially pertinent features in and
around exoplanets. These might be rings of
satellites above a planet’s equator—or even
structures surrounding a planetary sys-
tem’s star, put there to capture that star’s
light as a source of energy.
Even a single space station, were it big
enough, might be detectable using meth-ods similar to those employed to spot exo-
planets. A space station the size of Earth’s
moon (admittedly, a huge space station)
would stop enough of the light of its star
from reaching Earth to produce a percepti-
ble dip in that light. This “transit” method
is howKeplerspotted its prey and, as in-
struments improve, should one day be sen-
sitive enough to spot exomoons too. The
way to tell the difference between a moon
and a moon-sized space station, says Dr
Siemion, would be that the former would
orbit regularly whereas the latter might be
able to move around at will.
More standard searches for chemical
biosignatures could also be useful forseti.
A system of particular interest is Trappist-1,
40 light-years from Earth, where seven
rocky worlds orbit a red dwarf. Three of
these are within the star’s “habitable
zone”—a region where planets could have
liquid water on their surfaces.
The next generation of instruments will
reveal whether the planets in Trappist-1
have atmospheres or oceans. If there are at-
mospheres, they will also reveal what gases
are within them—possibly showing biosig-
natures of the sort Sagan spotted on Earth.
Meanwhile, the Breakthrough Listen
dataset continues to grow. In a study dis-
cussed in Seattle, a team of astronomers
used it to look for radio transmissions from
20 stars in the so-called “Earth transit
zone”—the part of the sky from which
Earth itself would be detectable by the tran-
sit method. The hypothesis is that, if intel-
ligent beings do exist in that region, they
might thus have discovered Earth and be
aiming transmissions at it. So far, the skies
have been quiet. Butsetiresearchers are
patient people. And they live in hope. 7I
nteractions with microbes in the soil
are crucial to the health of plants. Some
bacteria turn nitrogen from the air into am-
monia, and thence into nitrates, thus “fix-
ing” that element in a form which plants
can absorb and turn into proteins. Others,
by secreting antibiotics, protect plants
from pathogens. Others still, through the
formation of colonies called biofilms on
the surfaces of soil particles, help trap wa-
ter in the soil. And fungi, which consist of
long networks of hyphae that often pene-
trate plant roots, facilitate the uptake by
those roots of nutrients from the soil
Also this means that soil microbes af-fect crop yields. Indeed, they are one of the
most important influences on crop growth
that has yet to be exploited systematically
to raise those yields. But that will soon
change, if researchers who study the rhizo-
sphere, (as the zone of interaction between
plants’ roots and microbes is known) have
anything to do with it. This study is hard,
for the rhizosphere is a habitat as complex,
in its way, as a rainforest or a coral reef. It
just operates at a smaller scale. As a group
of researchers told the aaasmeeting in Se-
attle, the first step to understanding the
rhizosphere is therefore to simplify it.
Previous investigators have known this,
but have taken simplification too far, by
isolating and studying single microbes.
That, Jo Handelsman of the University of
Wisconsin–Madison told the meeting, is
where they have gone wrong. Soil microbes
interact. And mixtures of species can do
things individual bugs cannot manage. As
an example, she gave an ecological triangle
that her laboratory has been working on.
This triangle, which Dr Handelsman
calls thor(The Hitchhikers Of the Rhizo-
sphere), consists of three species, Pseudo-
monas koreensis, Flavobacterium johnsoniae
and Bacillus cereus. Each represents one of
three main bacterial phyla found in the
soil. Dr Handelsman, who was working on
P. koreensisas part of her research (it kills
organisms called oomycetes, which are se-
rious pathogens of plants) decided on this
trio because she found that when she tried
to isolate samples of her target organism
from the soil, the other two often came
along for the ride, as hitchhikers.
Her experiments with thorhave found
a strong interdependence between the
three. In particular, the stability of the tri-
angle depends on the fact that the Bacillus
protects the Flavobacterium by reducing
the production of antibiotics by the Pseu-
domonas. The advantage to its members ofSEATTLE
Studying relations between plants and
microbes will improve crop yieldsSoil microbiologyThree’s company
Putting down roots