Space Sunday: a touch of astronomy


Images of Proxima Centauri (l) and Wolf 359 (r) captured by NASA’s New Horizons spacecraft 7 billion km from Earth, are overlaid against images taken of the two stars from Earth-based telescopes, showing how the stars appear to “move” depending on the viewpoint. Credit: NASA

For the first time in history, a spacecraft has been used to demonstrate parallax as it applies to the stars – and in the process, underlining the fact that the constellations beloved of astrology are little more than a matter of line-of-sight as  seen from Earth.

The spacecraft in question is New Horizons, the mission that performed a fly-by of Pluto in 2016, and which is now some 7 billion kilometres from Earth – far enough to give it a unique view of the heavens around our solar system. On April 2nd/23rd, 2020 the spacecraft was commanded to turn its telescope on two of our nearest stellar neighbours, Proxima Centauri and Wolf 359 (a star doubtless familiar to Star Trek: The Next Generation), some 7.9 light years from Earth, to take pictures of both.

When compared to images of the two stars as seen from Earth, those from New Horizons clearly show how differently the two appear against the background of other stars when seen from different points of observation that are sufficiently far apart.

The New Horizons spacecraft. Credit: NASA

Use of parallax is a common astronomical exercise, used to measure the distance of stars from Earth. However, up until the New Horizons experiment, the average separation between points of observation have been opposite sides in Earth’s orbit around the Sun – or a mere 297,600,000 km apart when averaged out. That’s far enough to allow for an accurate measurements of other stars, but not far enough to show how differently a star might appear from different points in the sky.

It’s fair to say that New Horizons is looking at an alien sky, unlike what we see from Earth.nd that has allowed us to do something that had never been accomplished before—to see the nearest stars visibly displaced on the sky from the positions we see them on Earth.

– Alan Stern, Principal Investigator, New Horizons

For the experiment, the images from New Horizons were compared with images captured by the Las Cumbres Observatory, Panama, operating a remote telescope at Siding Spring Observatory in Australia, and from the Mt. Lemmon Observatory in Arizona, both of which imaged the stars on the same night as New Horizons captured its images, so as to provide a direct comparison.

Witnessing the Birth of Stars

The Rho Ophiuchi cloud complex is a dark nebula of gas and dust that is located 1° south of the star ρ Ophiuchi in the constellation Ophiuchus. Some 460 light-years from Earth, it is one of the closest and active start-forming regions to the Sun.

It’s called a “dark nebula” because the dust cloud is so dense, visible light from stars within it is almost completely obscured. However, astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have found something of interest within the cloud.

Two infra-red images of the Rho Ophiuchi nebula showing the IRAS 16293 system within it, as captured by ALMA showing (l) what was thought to be a binary system of stars (A and B), and a closer view of A (r), revealing its own binary nature. The two stars of A re some 54 AU apart. All three stars are surrounded by accretion disks, with the energised dust surrounding the A stars also visible. Credit: Maureira et al

The item in question is IRAS 16293-2422, a system that has a long history of being observed in the infra-red. However, it had been thought the system comprised a binary pairing of protostars, simply referred to as A and B some 700 AU apart. However, the new study has revealed that the star known as A is actually itself a pair of stars, now called A1 and A2. They are both of similar in mass to the Sun – A1 being slightly smaller, and A2 around 1.4 times larger, and each is surrounded by its own accretion disk from which it is drawing material.

These stars and their disks have certain fascinating aspects. The first is that they are only separated by a distance slightly greater to that of Pluto when at aphelion relative to Earth. They also complete an orbit around one another one every 360 terrestrial years. In addition, the accretion disks around A1 and A2 are also unique.

Detailed view of the binary protostar system within IRAS 16293-2422 and with a size comparison to our solar system. The separation between the sources A1 and A2 is roughly the diameter of the Pluto orbit. The size of the disk around A1 (unresolved) is about the diameter of the asteroid belt. The size of the disk around A2 is about the diameter of the Saturn orbit. Image Credit: © MPE

Both disks are extremely active, filaments of matter streaming into the stars at the heart of each, and further filaments of dust flowing into the disks from the nebula. In addition, the disk around A2 disk appears to be oddly inclined compared to the disks around A and the more distant B, suggesting complex interactions may be at play around it. The disk also appears to have parts rotating in opposite directions relative to one another, the first time such a phenomenon has been seen in a protostar accretion disk. It suggests that should planets eventually form around the star, those nearer to it may orbit the opposite direction to those further out.

Organic scans of the disk also detected glycolaldehyde — a simple form of sugar – and Chloromethane, also called methyl chloride, an important biomarker, together with Carbon Sulphide, Isocyanic Acid, Formamide, and Formic Acid. The presence of the organics is important as it shown that the basic building blocks of life can exist within the accretion disks around stars, and so may be available when the remnants of that disk forms planets.

It’s not clear if / when the formation of either star may reach a point of nuclear ignition, or how such an event might affect the other. However, their confirmation provides astronomers with a first-hand opportunity to witness the earliest stage in the process of stellar evolution.

Proxima Centauri c Confirmed

In August 2017 I wrote about the discovery of Proxima Centauri b, a planet situated within the habitable zone around Proxima Centauri, 4.25 light years away from Earth (see: Space Sunday: exoplanets, dark matter, rovers and recoveries). More recently, in January 2020, I noted that the star may have a further planet orbiting it (see: Space Sunday: commercial crew test flights & exoplanets). Now, astronomers have confirmed the existence of that second planet, Proxima Centauri c, sitting well outside the star’s habitable zone.

Proxima Centauri b was discovered via a combination of both the transit and radial velocity methods – but follow-up observations suggested that the “wobble” in Proxima Centauri’s orbit appeared to be greater than could be accounted for by a planet of Proxima Centauri b’s estimated size, suggesting that a further planet may be present – although the team responsible for the discovery at the time requested others check their data and the star to help positively eliminate any misidentification of stellar phenomena that may have been made.

Now an extensive study of the star, coupled with a review of past observations have helped confirm the existence of Proxima Centauri c – referred to as PC c. In particular, a team of astronomers worked back through data on past observations of the Proxima Centauri system that identified three distinct data sets that have in turn allowed the orbit of the planet and its possible mass to be constrained.

The team of astronomers estimate that PC c has a mass of somewhere between 7 times that of Earth and 0.8 that of Jupiter. This puts it in the category of either a sold “super-Earth” planet or a gas giant planet. It orbits its parent star every 5.2 terrestrial years, at a distance of around 1.5 AU. Due to its large distance from Proxima Centauri, the exoplanet is unlikely to be habitable, with a low equilibrium temperature of around 39º K or -234.15º C.

While the planet may appear to be relatively close to its Sun, the fact that Proxima Centauri is only 15% the radial size of the Sun (with 12% of its mass) means that PC c is potentially an ideal candidate for direct observation by the James Web Space Telescope or the Nancy Grace Roman Space Telescope, once these have been launched later this decade.

Launches Delayed

NASA has announced that the launches of both the Perseverance Mars Rover and the James Webb Space Telescope (IWST) have been delayed.

A launch vehicle processing “hiccup” has delayed the launch of the rover by three days to back next month’s launch by three days to Monday, July 20th, 2020. The launch window will open at 14:15 UTC and extends through until August 11th, 2020.

The James Webb Space Telescope – launch delayed until after March 2021. Credit: NASA

JWST, meantime has seen its planned March 2021 launch date pushed back further into the year. The decision to reschedule was made on June 2nd, and comes primarily as a result of the SARS-CoV-2 pandemic interfering with mission preparations.

However, the amount of “reserve” time – time set aside to specifically allow for delays in mission preparations – had already reached a level where the March launch date was already in doubt, leading to the possibility of it being pushed back. Now the concern is that when operations eventually ramp back up, there may be further delays that impact the schedule beyond those caused by the pandemic, so the decision has been made in advance to look to a date later in 2021 on which to launch, although no date has yet been confirmed.

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