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 Dune, or oceanic, without landmass. 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 the telescope hubble still active and the James Webb Sending back extraordinary stellar views, NASA begins to consider an even more ambitious project. Its creators have named it Habitable Worlds Observatory (HWO, for its acronym in English) and its objective is divided equally between advanced astrophysical research and something almost unthinkable: the photography of the surfaces of extrasolar planets.
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. Today it is conceived as a telescope with a diameter of four meters (almost double that of the hubble but less than him Webb) dedicated to studying the bands of ultraviolet, visible and near infrared light.
Its size will allow it to be accommodated in the hood of a conventional rocket, without the need to fold it as was the case with the Webb. The one-piece mirror will have to be manufactured to tolerances a thousand times tighter, as it will detect visible and ultraviolet radiation, with wavelengths shorter than infrared. Preliminary studies suggest that polishing should remove any irregularities greater than a billionth of a millimeter, less than the diameter of an atom.
Such a mirror is very fragile. Any impact of a speck of dust would cause an irregularity that translates into an unwanted scattering of light, which would degrade the observations. So the new telescope will be more like the hubble what to Webb: a metal tube that protects the optical system and prevents the entry of stray light.
But even with the best mirror, detecting (and photographing) such remote planets is very difficult, since they move in the brightness of their star. For this reason, all the satellites used for this work use a small opaque disk that hides the star, avoiding glare and showing only the tiny points of light that revolve around it.
The future HWO will also have a glare blocker albeit on a much larger scale. It will be a parasol (or, better, parastar) fifty meters in diameter that will fly in formation with the telescope… almost 100,000 kilometers away. It will be launched folded, of course, but once opened it will take the shape of a huge flower with a 25-meter circular core surrounded by twenty “petals” reminiscent of those of a sunflower.
This form is not whimsical. Many simulations have been carried out to determine the best design of the petals whose mission is to reduce the scattered light around the central disk. Ideally, they should have been semi-transparent, with progressive opacity, but in the end manufacturing difficulties made it advisable to make them completely dark. The edge of each petal is metallic, with a very delicate polish and even the curvature of the tip of each segment has been calculated to reduce stray light as much as possible.
According to its designers, opening the sunshade in space will not be as difficult a task as it seems. Technologies that already exist will be used. Specifically, the same ones that allow the large antennas of some communications satellites to be deployed. One of them, suitable for 30-meter antennas, has already been successfully tested at least six or seven times (probably more if we include military satellites, but those experiments are not talked about) so extending the sunshade with its petals should not present difficulties.
The telescope and its sunshade will be anchored in an orbit around the L1 Lagrange point, one and a half million kilometers from Earth. It is the same area where they orbit the Webb and other satellites. 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.
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 signs compatible with life could be detected in about 25 near-Earth bodies (“nearby” here implies tens of light-years away). Others, more pessimistic, aim to characterize (that is, study its surface) two or three planets similar to ours.
The viability of this pharaonic project depends on financing. So far, NASA only has $1.5 billion approved for all of its astrophysics projects 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 the experience of Webb It does not help, that figure can double over the almost twenty years that the project will last. At best, the first photographs of the surface of other worlds will not arrive until well into the next decade.
You can follow MATTER in Facebook, Twitter and instagramor sign up here to receive our weekly newsletter.
Subscribe to continue reading
Read without limits
#flowershaped #telescope #NASA #photograph #habitable #worlds