The LUVOIR Telescope: Telling the story of life in the cosmos
A few weeks ago was published the Pathways to Discovery in Astronomy and Astrophysics for the
2020s - or Astro2020: a document of the National Academies of Sciences of the United States
that every 10 years suggests the objectives of astronomical research for the next decade,
presenting an ambitious program of terrestrial and space activities to be developed.
Government agencies such as NASA and the National Science Foundation rely on this "survey",
the result of the opinion of dozens of experts, to decide how to allocate public funding
and other resources for astrophysical research in the next decade and beyond.
For Astro2020, the absolute priority objective is the search for life on extrasolar planets,
and to achieve this goal it considers necessary the development of a new space program,
heir to NASA's Great Observatories Program, which allowed to launch in space from 1990 to 2003
four space telescopes, starting with Hubble. According to Astro2020, the available resources
must be focused on a space telescope with a primary mirror of at least eight meters
in diameter, optimized for infrared but capable of observing across the spectrum,
from infrared to ultraviolet. The future telescope - called for now LUVOIR, from Large Ultraviolet
Optical Infrared Surveyor, and for which there is also an option with a fifteen-meter mirror
(LUVOIR-A), should be ready for launch in the early 2040s and will be tasked with
looking for biological signs in the atmospheres of exoplanets thought to be potentially habitable.
If you take into account the size of the mirror and the focal length of
Hubble - optical properties that are the basis of any objective assessment of a telescope's
capabilities - you can easily calculate that "the space telescope par excellence",
operational since 1990, can resolve objects up to angular resolutions of just 0.04 seconds of arc,
just over a hundred-thousandth of a degree. This is like saying that Hubble could distinguish
two fireflies 5000 km away and only 1 meter apart! Various observing campaigns, such as Hubble Deep
Field, Ultra Deep Field, and eXtreme Deep Fields, have used these capabilities to reveal what lies
hidden in the depths of deep space: thousands upon thousands of galaxies in tiny regions of space
covering mere fractions of a millionth of the sky. Yet, even at its maximum capabilities - even
with the equivalent of a month of continuous observation - Hubble can only see about 10 percent
of the galaxies that are out there. Moreover, even most of the galaxies that are revealed
are little more than a point of light, because Hubble's mirror is relatively modest in size,
with too little resolving power to reveal very fine details. Hubble represents in many
ways the greatest astronomical feat ever undertaken by our civilization,
but it is also fundamentally limited in size. Picking up its legacy will be the James Webb
Space Telescope, which will launch on December 18 from ESA's base in Guyana. Webb is larger and
"colder" than Hubble, and can therefore investigate at much longer wavelengths
In 2027, the Nancy Roman Telescope will also launch,
which is as large as Hubble, but with a 5° square field of view and much more advanced cameras.
These observatories will begin to address some of the questions Hubble cannot answer.
With its huge sunshade, its location well beyond Earth and the Moon, its cooler, and its 6.5-meter
gold-coated primary mirror, James Webb will outperform Hubble on many fronts. Observing
at a wavelength 15 times longer than Hubble's, thanks to cooling, will in fact allow it to
penetrate dust more easily and reveal a wealth of details about planet formation and the atmospheric
composition of Earth-like planets. It will really be a huge step forward for space astronomy.
Instead, the Nancy Roman Telescope will have a 2.4-meter mirror, like Hubble, but with the
ability to operate in a wider spectrum, including the near-infrared. And much, much faster.
Everything Hubble does in months of work, Roman will be able to do in hours!
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But even with these cool new space toys, many questions will remain unanswered.
The Webb Telescope, no matter how extraordinary its capabilities may be,
will never be able to show us directly a rocky planet the size of Earth. Nor will it be able
to tell us if the planet could be inhabited. The fact is, despite all the excitement that
has surrounded the search for exoplanets in recent years, the more than 4,500 planets found so far
have been invisible actors on the cosmic stage. Except for a handful of gas giants
imaged by ground-based telescopes, virtually all exoplanets have been detected only indirectly,
either through the brightness decrease induced by their passage in front of their star's disk
or through oscillations in the star's position induced by the planet's mass.
Fortunately, even with so little data available astronomers are able to determine the orbit,
radius, mass, and sometimes density of an exoplanet, but not much else. Extrasolar
planets still remain, in the words of one researcher in the field, "little black shadows."
But astronomers want much more than that. They would like to know in detail the chemical
composition of the planets' atmospheres, to know whether liquid water exists on their surfaces
and, ultimately, whether these worlds might be hospitable to life.
Well... To answer these questions, Decadal Survey for Astronomy and Astrophysics
has selected the most ambitious, the most complex, the most expensive, and the most revolutionary
space telescope ever conceived, it is called LUVOIR, for Large UV/Optical/IR Surveyor.
The "small," 8-meter version, called LUVOIR-B, is designed to produce
angular resolution 5-10 times better than the James Webb Space Telescope and a sensitivity
limit of up to 2,000 times better than the HST. The "large," 15-meter version, called LUVOIR-A,
will search for habitable conditions and signs of life on dozens of potentially habitable worlds
beyond our Solar System. The results of this research will provide a wealth of data on the
atmospheric composition and surface conditions of rocky planets in the habitable zones of a
variety of stars. These data will revolutionize our understanding of planetary-scale habitability
and allow the first assessments of how often global biospheres
arise on habitable worlds. Safe detection of life requires access to a wide range of molecules,
which requires direct spectra with broad coverage of wavelengths from near UV to near-infrared.
The idea of a very large space telescope capable of seeing through many wavelengths
has been discussed and even proposed at NASA for nearly two decades. But the technology
needed to fold a large segmented mirror and build a high-performance coronagraph
was lacking until recently, as was the science behind biosignature detection and recognition.
If LUVOIR-A becomes reality it would provide a never-before-experienced view of the Earth-like
exoplanets we have already discovered and will discover in the coming years.
Now, these planets are in fact just dark spots on the star around which they revolve.
A telescope like this would completely change our view of these planets by providing a more
general view and allowing statistical analysis of such planets in the universe.
The change would be similar to what the Kepler telescope did with the discovery of exoplanets.
Kepler from the 1990s until now has discovered so many exoplanets
that it has allowed statistical analyses of how many of them are rocky
or gas giants and around what kind of stars they can be found. This has completely
changed astronomical research by allowing large-scale analyses and considerations.
Scientists will be able to read the contents of exoplanets' atmospheres like
never before with the Extreme Coronagraph for Living Planetary Systems (ECLIPS), which
will be able to detect compounds such as oxygen, ozone, water vapor, carbon dioxide, and methane...
all indicators of biological processes in action. LUVOIR-A will then be able to capture the
variation in brightness - due to their rotation - of most rocky planets.
This will allow to know the length of their day. But that's not all! By observing the variation
of light in more than one wavelength, it will likely be able to determine the
percentages of landmasses, oceans, and cloud cover. as well as detect seasonal changes.
The project team is proposing LUVOIR with a diverse and independent set of instrumentation and
capabilities. The telescope will be flexible and able to address various fields of astrophysics.
These range from the study of dark matter to the functioning of galaxies. LUVOIR-A for example will
also be able to monitor the development of geysers on Europa and Enceladus or to photograph Jupiter
with the same detail of the images taken in recent years by the Juno probe, show us the
surface conformation of Pluto and Eris ... There are still many things to discover and
understand about the bodies within the Solar System. LUVOIR-A can provide up to about 25
km of visible light imaging resolution for the Jupiter system, allowing detailed monitoring of
the atmospheric dynamics of Jupiter, Saturn, Uranus, and Neptune for long time scales.
Sensitive, high-resolution imaging and spectroscopy of comets, asteroids, moons,
and objects in the Solar System's Kuiper belt that will not be visited by spacecraft in the
near future can provide vital information about the processes that formed the Solar System.
Not to mention that the search for life can also be done closer to home.
In fact, in recent decades, we have discovered that several moons in the outer Solar System,
such as Europa and Enceladus, have liquid water beneath their icy surfaces
So far, LUVOIR-A is the largest space telescope that can be built and launched from the ground...
In fact, its 15-meter mirror is the maximum size that can fit the next generation of heavy rockets,
whether it's NASA's Space Launch System or the SpaceX Starship.
Folded inside the rocket at launch, the observatory would be sent into space, as it will
be for the Webb Telescope, at a gravitationally stable point called Lagrange Point 2.
During the design process, the idea of assembling LUVOIR-A in space, after launching its various
parts into orbit, was also considered. The advantage would have been to be able to equip
it with a mirror much larger than 15 meters; but NASA has decided that, at the moment, the
assembly in space done by astronauts is neither technically possible nor economically convenient.
And speaking of money... LUVOIR will still be a very expensive toy, with estimates ranging from
$18 billion to $24 billion for the 15.1-meter version to $15 billion for the 8-meter version.
The staff that presented the project invites the comparison with the 20 billion "burned" by Hubble
between design, construction, and maintenance during its 30 years of life ... And indeed,
the balance of costs and benefits seems to lean on the side of LUVOIR-A.
All extraordinarily exciting, then ... if it were not for two small details. The project
talks about 2040, which is like saying "in a thousand years". Twenty years seems like a
long time, and the disappointment for such a long wait could dampen our enthusiasm.
My impression, however, is different. I think that after the experience with Hubble and
Webb Telescope, the LUVOIR design will not have to start from scratch, and therefore the time
can be halved. Of course, you have to want it! The second detail? Well... the fear that some
zealous government official will come up with the idea of "saving money" on funding.
The U.S. Congress and NASA should not dare to make their choice fall on the
8-meter version... That would be a huge mistake! Only LUVOIR-A would answer the biggest questions
we have about our Universe. All we have to do, to realize our dreams of knowing what is out
there in the Universe, is to choose to build it. LUVOIR-A is the only space observatory that could
revolutionize astronomy over and over again, perhaps for the rest of the 21st century.