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With its superior spatial resolution the Colossus will be able to make revolutionary discoveries in all areas of astrophysics and space exploration. Here are only a few representative examples which demonstrate the power of the Colossus.
Detecting Habitable Planets
The Solar system analogues with all the planets down to Mercury can be resolved as far from the Sun as 100 light years. Thus, the reflected light can be detected directly through imaging from hundreds of planets, from Jupiter-like to Earth-like. Tools like spectroscopy and spectropolarimetry can be used to analyze this light. This will dramatically improve our knowledge on exoplanetary atmospheres, of which we know now no more than a dozen. The detection of habitable planets will be a reality.
Figure 2.1. The inner Solar system (only terrestrial planets) as seen at 50 light years away from the Sun by the Colossus. The Sun to Mars distance will be seen at the angle of about 100 milliarcseconds. The sizes of the planets and the Sun on this image are not scaled with the distance.
Seeing the Surfaces of other Stars
The Sun is the only star whose surface we can currently investigate directly with the spatial resolution of somewhat smaller than 100 km. The most prominent features in the visible are dark magnetic sunspots whose cycle strongly influences interplanetary environment in the Solar system. Using indirect methods we can figure out that magnetic spots of even larger sizes are in principle present on all solar-type stars and those that are cooler. The Colossus will be the first telescope and other activity phenomena directly on stellar surfaces. Thus, solar physics will get to study other stars and compare them directly with the Sun. This breakthrough is comparable to the first observations of sunspots using a telescope by Galileo.
Figure 2.2. The solar disk with sunspots as seen by by the SOHO satellite (left) and the Colossus (right) at the distance of the nearest Sun-like star α Cen A (8.5 mas angular diameter). The magnetic spots can be traced directly on the stellar disk for the first time.
Figure 2.3. The disk of the cool supergiant Betelgeuse (α Ori, 56 mas angular diameter): obtained by the Hubble Space Telescope in the UV and revealing a mysterious hot spot on the stellar surface (left), simulated from a model by Freytag (2002) (middle) and as expected to be seen by the Colossus (right).
Seeing Near Black Hole Event Horizon in Galaxy Center
The Colossus will resolve stars falling into the super-massive black hole in the Galaxy center very close to its event horizon. This will be the closest encounter with a black hole ever and the first direct probe of a perturbed space-time near the event horizon.
Figure 2.4. The 1"x1" image of the Galaxy center black hole environment obtained at ESO/VLT with the angular resolution of 60 mas in the infrared (left, Gillessen et al. 2008). The Colossus will enable detection of individual stars falling into the black hole down to its event horizon at 10 μas.
Monitoring Moon Colonization
The Colossus will be able to detect objects and details on the lunar surface as small as 2m. This is comparable with (3x) the resolution of the Lunar Reconnaissance Orbiter Camera (LROC, NASA) which was able to detect from its lowest orbit the Apollo landing sites and tracks left by astronauts (Fig. 2.5).
Figure 2.5. The landing site of the Apollo 17 mission and track left by astronauts photographed from the space by the Lunar Reconnaissance Orbiter Camera (LROC, NASA) on the low orbit (top, horizontal size of the image is about 400m on the lunar surface) and as seen by the Colossus from the Earth surface (bottom).
Manmade Objects in Space
The Colossus will be able to see millimeter-scale details of manmade objects in space on geocentric orbits. An example is shown in Fig. 2.6.
Figure 2.6. A part of the International Space Station (ISS) photographed from space during repair of the US Solar array by astronaut Scott Parazynski anchored on the end of the OBSS (NASA). The Colossus will be able to see manmade objects at this height with the level of detail as on this picture - the spatial resolution of 2mm at the height of 400km is about or smaller than the line thickness of the numbers in the top-left corner.