The telescope with which NASA wants to find habitable worlds

More than 5,000 exoplanets are known.

Almost three hundred fulfill the conditions to support some form of life: they are rocky bodies, not gas giants, that their star is not wildly active and that they orbit it at a distance suitable for its temperature to allow the existence of liquid water.

Until now, all this planetary pleiad has been detected by analyzing small variations in the brightness of the star.

In some cases they have been photographed as simple luminous dots in images obtained from ground observatories.

We do not know any characteristics of its surface.

They can be desert worlds, like Arrakis from

, or oceanic, with no landfills.

Chemical compounds (methane, carbon dioxide and even oxygen) have been detected in some, but in general they are giant planets, hardly suitable for hosting life.

Now, with

still active and

returning extraordinary stellar vistas, NASA is beginning to consider an even more ambitious project.

Its creators have named it the Habitable Worlds Observatory (HBO for its acronym in English) and its objective is divided equally between advanced astrophysical research and something almost unthinkable: the characterization (in other words, the analysis) of their atmospheres.

Maybe even biomarker detection.

The HWO is still in the preliminary design phase, although some researchers have been testing components that will one day fly into space for more than two years.

Until last week, NASA had on the table two proposals for telescopes for the study of exoplanets.

In the end, he has merged both into one.

Today it is envisioned as a 20-foot-diameter telescope (almost the same as the

) dedicated to studying the ultraviolet, visible, and near-infrared bands of light.

To accommodate it in the rocket hood, it will be necessary to fold its mirror, as was the case with the

.

It will have to be manufactured to tolerances a thousand times tighter, since it will detect visible and ultraviolet radiation, of shorter wavelengths than infrared.

Preliminary studies suggest that polishing should remove any irregularity greater than a billionth of a millimeter.

That is, dimensions of the order of atomic diameter.

Such a mirror is very fragile.

Any impact from a speck of dust would cause an irregularity that results in unwanted scattering of light and degrades the observations.

For this reason, one of the discarded projects was more like Hubble: a metallic tube that would prevent stray light from entering the optical system.

The chosen design, more reminiscent of the

, features a main mirror installed and protruding above a large drop-down sun visor, leaving the large reflector more exposed.

Even with the best mirror, detecting - and photographing - such remote planets is very difficult, since they move immersed in the brightness of their star.

That is why all the satellites used for this work use a "coronagraph".

In essence, it is a small opaque disk that hides the star, avoiding glare and showing only the tiny points of light that revolve around it.

It is a process that demands immense precision.

The telescope must be pointed exactly towards the center of the star.

Under these conditions, the light from a possible planet will reach it at an angle of almost zero degrees, but not quite zero.

Detecting that minimal difference requires complicated optical systems and, of course, enormous stability of the telescope itself.

One of the discarded projects used a gigantic glare blocker: a kind of parasol (or, better, “parastar”) fifty meters in diameter that would fly in formation with the telescope almost 100,000 kilometers away.

Although small-scale tests had been done, it was deemed too risky and the selection fell on the other option: a more conventional coronagraph housed within the telescope's optical system.

A series of masks will allow it to be adapted to suppress the luminosity depending on the star being observed.

The telescope will be anchored in an orbit around the Lagrange point L2, one and a half million kilometers from Earth.

It is the same area where the Webb and other satellites orbit, but there is no danger of collision.

The space is very big.

At that distance, the repair of any fault is currently impossible.

But in the design of the HWO, the possibility of receiving the visit of maintenance and refueling robots is contemplated, which would extend its useful life.

Many of the teams on board will build on the experience gained with

and

, but enormous challenges remain to be resolved.

For example, the tolerances in the mechanical adjustment of the mirrors, which will have to be measured in nanometers.

Or the methods to guarantee absolute stability despite all possible disturbances, from the gravitational influence of other stars to mere thermal expansions of the structure.

And, in addition, there is the problem of technological obsolescence.

By the time the telescope is launched it is certain that many of its components, selected many years before, will already be out of date.

The only solution is the one that has been decided: Being able to send robotic probes not only to carry out maintenance tasks, but also to change the observation instruments for newer ones.

What results can be expected?

The answer can only be based on statistics, based on the number and nature of the exoplanets detected so far.

Some estimates suggest that the atmospheric composition of about 25 Earth-sized planets close to us could be detected ("close" here implies tens of light-years away).

Others, more pessimistic, aim to characterize only two or three.

The viability of this program depends on funding.

So far, NASA only has $1.5 billion approved for all of its Astrophysics activities for the fiscal year (almost 5% less than last year).

A very conservative estimate of the cost of the HWO telescope is around $10 billion.

But if

's experience is anything to go by, that figure may double over the nearly 20-year life of the project.

In the best of cases, the first results will not arrive until after 2040. Something that does not satisfy astronomers too much: some fear that by the time the HWO flies they will already have entered retirement.

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