New Telescope Array to Probe Solar System's Fringes

At the National Astronomical Observatory of the Sierra de San Pedro Mártir (OAN-SPM), run by the Astronomy Institute (IA) of the UNAM, it will be possible to detect, starting in early 2025, trans-Neptunian objects that pass in front of the observed stars.

To do so, the observation technique known as stellar occultation will be used, thanks to the international TAOS II project (Automated Census of Occultations by Trans-Neptunian Objects), which includes three robotic telescopes installed at that location.

The work will provide key information about the formation and dynamic evolution of our solar system and about the mechanism that perturbs those in the Kuiper Belt (that ring of rocks, ice and dwarf planets located beyond Neptune, whose most famous element is Pluto) towards cometary orbits.

The detection of the majority in that region had been impossible due to its low luminosity, even for the largest telescopes. Now it will be a reality with the participation of the Ensenada headquarters of the IA; the Academia Sinica (Institute of Astronomy and Astrophysics) of Taiwan; the Harvard-Smithsonian Center for Astrophysics; and the Canadian Astronomy Data Center.

Approximately 4.5 billion years ago, from a dense cloud of interstellar gas and dust, our system was formed. But the process of creating planets, including Earth, was not 100 percent efficient and a “pile of crumbs” remained, rocks that were partly ejected into interstellar space, and others that remained “trapped” in the outermost part, in the Kuiper belt.

These trans-Neptunian objects are a “relic,” said the head of the project in Mexico, Mauricio Reyes Ruiz. “If we measure their characteristics, we will have very important ‘pieces’ to understand how they formed.” Hence the importance of these studies.

TAOS II is designed to determine how their distribution is in terms of their size and orbits; “that is basically what we are going to do,” added the IA researcher in an interview.

The doctor in Space Physics and Astronomy clarified that this is the continuation of a project, TAOS I, also international, which began in the early 2000s at the Lulin Astronomical Observatory, Taiwan, to test an old observation technique, but which has regained importance and power thanks to technological advances: stellar occultations.

UNAM received the invitation to participate in the second part due to the interest in installing the telescopes at the OAN-SPM, being one of the best places in the world for astronomical observation due to its infrastructure and capacity of its academic staff. “In 2010 I joined and we started working,” Reyes Ruiz recalled.

With TAOS II, “we will observe a very large number of stars, around 10,000 simultaneously, to detect whether a rock - which can measure from one to several kilometers - orbiting beyond the orbit of Neptune is passing in front of any of them.” This monitoring will be carried out for at least five years, he said.

Doctor in Optoelectronics, Joel Humberto Castro Chacón, also a member of the team and a researcher assigned to the IA, pointed out that the three robotic telescopes, whose main mirror measures 1.3 meters in diameter, are synchronized so that they observe the same area of ​​the sky to obtain the simultaneous measurement of the brightness of those 10 thousand stars.

In this case, he pointed out, the fundamental part of the system is its cameras and detectors, which were designed exclusively for this project under specific characteristics and requirements; for example, they have detection zones that measure 15 by 15 centimeters, with 80 megapixels; for reference, the detector of a mobile phone camera measures five millimeters.

In addition, the expert explained, they can “read” up to 100 images per second. “We are going to work at a speed of 20 images per second, that is, the 10 thousand stars are going to be observed with three telescopes 20 times per second,” because the duration of the stellar occultation phenomena is, for objects in the Kuiper Belt, approximately 0.2 seconds.

The interesting thing about occultations, said Castro Chacón, is that we do not see the rocks in front of a star, but rather we detect that its brightness decreases. It is estimated that, with luck, it could take 100 years to find an occultation by seeing a single star without blinking; without luck, it could take 10 thousand years.

To improve the probabilities, we will observe 10 thousand suns at the same time, which will give us a few dozen events per year, enough to build models of the formation and evolution of the solar system and meet our main goal, he explained.

TAOS II is a very complex system, where the three telescopes must operate alone and synchronize themselves, while monitoring the temperature and humidity of the environment, as well as the temperature and internal pressure of the cameras, all of which are essential for the images to have good quality. The movement systems and the domes are also determined by a master control software.

The amount of data that will be generated is so large (two or three terabytes per night, equivalent to the same number of laptops) that a special place is needed to store it. For this, the Ensenada headquarters of the IA has a massive center, the first of its kind in the northwest region of the country.

To date, it has the capacity to operate for the first two years, and it must grow to capture the information obtained over the five years of the duration of the work.

Likewise, said Joel Castro, there is collaboration with the University of Victoria, Canada, to have a copy of the one that is in that institution, a safekeeping, and to improve its access by the participating entities.

At the moment, the hardware and the electronic and mechanical parts of TAOS II are operating in the test phase. Work is being done on the final part of the control software, codes and programs that will allow the telescopes to operate remotely at first, and then robotic (autonomous) at the beginning of next year.

We are obtaining a large amount of relevant information and with it, we will even be able to search for planets outside our solar system or study stellar variability, emphasized the scientist assigned to UNAM.