Astronomers research on radioactive aluminum in solar systems unlocks formation secrets

Washington D.C., Jul 21: The rediscovery of a lost planet could pave the way for the detection of a world within the habitable 'Goldilocks zone' in a distant solar system.

The planet, the size, and mass of Saturn with an orbit of 35 days is among hundreds of 'lost' worlds that University of Warwick astronomers are pioneering a new method to track down and characterise in the hope of finding cooler planets like those in our Solar System and even potentially habitable planets.

Reported in Astrophysical Journal Letters, the planet named NGTS-11b orbits a star 620 light-years away and is located five times closer to its sun than Earth is to our own.

The planet was originally found in a search for planets in 2018 by the Warwick-led team using data from NASA's TESS telescope. This uses the transit method to spot planets, scanning for the telltale dip in light from the star that indicates that an object has passed between the telescope and the star. However, TESS only scans most sections of the sky for 27 days.

This means many of the longer period planets only transit once in the TESS data. And without a second observation the planet is effectively lost. The University of Warwick-led team followed up one of these 'lost' planets using the telescopes at the Next-Generation Transit Survey (NGTS) in Chile and observed the star for seventy-nine nights, eventually catching the planet transiting for a second time nearly a year after the first detected transit.

"By chasing that second transit down we've found a longer period planet. It's the first of hopefully many such finds pushing to longer periods. These discoveries are rare but important since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own solar system," said Dr. Samuel Gill from the Department of Physics at the University of Warwick.

"NGTS-11b has a temperature of only 160°C -- cooler than Mercury and Venus. Although this is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets which typically have temperatures above 1,000°C," added Gill.

The Goldilocks zone refers to a range of orbits that would allow a planet or moon to support liquid water: too close to its star and it will be too hot, but too far away and it will be too cold.

"This planet is out at a thirty-five days orbit, which is a much longer period than we usually find them. It is exciting to see the Goldilocks zone within our sights," said Co-author Dr. Daniel Bayliss from the University of Warwick.

"The original transit appeared just once in the TESS data, and it was our team's painstaking detective work that allowed us to find it again a year later with NGTS," said Co-author Professor Pete Wheatley from the University of Warwick.

"NGTS has twelve state-of-the-art telescopes, which means that we can monitor multiple stars for months on end, searching for lost planets. The dip in light from the transit is only 1 percent deep and occurs only once every 35 days, putting it out of reach of other telescopes," added Wheatley.

"There are hundreds of single transits detected by TESS that we will be monitoring using this method. This will allow us to discover cooler exoplanets of all sizes, including planets more like those in our own solar system. Some of these will be small rocky planets in the Goldilocks zone that are cool enough to host liquid water oceans and potentially extraterrestrial life," said Dr. Gill.

Massachusetts, Jul 27: Scientists from the Centre for Astrophysics, Harvard and Smithsonian and the New Jersey Institute of Technology on Monday announced the first successful measurement and characterisation of the 'central engine' of a large solar flare.

The findings have been published in the journal Nature Astronomy, reveal the source of the intense energy powering solar flares.

According to the study -- which closely examined a large solar flare accompanied by a powerful eruption captured on September 10, 2017, by the NJIT's Owens Valley Solar Array (EOVSA), at microwaves -- the intense energy powering the flare is the result of an enormous electric current 'sheet' stretching more than 40,000 kilometres -- greater than the length of three Earths placed side-by-side -- through the core flaring region, where opposing magnetic field lines approach, break, and reconnect.

"During large eruptions on the Sun, particles such as electrons can get accelerated to high energies. How exactly this happens is not clearly understood, but it is thought to be related to the Sun's magnetic field," said Kathy Reeves, astrophysicist, CfA, and co-author of the study.

"It has long been suggested that the sudden release of magnetic energy through the reconnection current sheet is responsible for these major eruptions, yet there has been no measurement of its magnetic properties," said Bin Chen, professor of physics at NJIT and lead author on the study.

"With this study, we have finally measured the details of the magnetic field of a current sheet for the first time, giving us a new understanding of the central engine of the Sun's solar flares," added Chen.

Measurements were taken during the study also indicate a magnetic, bottle-like structure located at the top of the flare's loop-shaped base, or flare arcade, at a height of nearly 20,000 kilometres above the surface of the Sun. The study suggests that this is the primary site where a solar flare's highly energetic electrons are trapped and accelerated to nearly the speed of light.

"We found that there were a lot of accelerated particles just above the bright, flaring loops," said Reeves.

"The microwaves, coupled with modeling, tells us there is a minimum in the magnetic field at the location where we see the most accelerated particles, and a strong magnetic field in the linear, sheet-like structure further above the loops," added Reeves.

The sheet-like structure and the loops seem to be working in concert, with significant magnetic energy being pumped into the current sheet at an estimated rate of 10-100 billion trillion joules per second, and 99 percent of the flare's relativistic electrons were observed congregating at the magnetic bottle.

"While the current sheet seems to be the place where the energy is released to get the ball rolling, most of the electron acceleration appears to be occurring in this other location, the magnetic bottle," said Dale Gary, director, EOVSA and co-author on the study.

"Others have proposed such a structure in solar flares before, but we can truly see it now in the numbers. What our data showed was a special location at the bottom of the current sheet -- the magnetic bottle -- appears to be crucial in producing or confining the relativistic electrons," Chen said.

The study results were achieved through a combination of microwave observations from EOVSA and extreme ultra-violet imaging observations from the Smithsonian Astrophysical Observatory's Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO).

The observations were combined with analytical and numerical modeling -- based on a 1990s theoretical model of solar flare physics -- to help scientists understand the structure of the magnetic field during a large solar eruption.

"Our model was used for computing the physics of the magnetic forces during this eruption, which manifests as a highly twisted 'rope' of magnetic field lines, or magnetic flux rope," said Reeves.

"It is remarkable that this complicated process can be captured by a straightforward analytical model, and that the predicted and measured magnetic fields match so well," added Reeves.

Performed by Chengcai Shen, astrophysicist, CfA, the simulations allowed the team to resolve the thin reconnection current sheet and capture it in detail.

"Our simulation results match both the theoretical prediction on magnetic field configuration during a solar eruption and reproduce a set of observable features from this particular flare, including magnetic strength and plasma inflow/outflows around the reconnecting current sheet. It is a powerful tool to compare theoretical expectations and observations in detail," said Shen.

For the team, the study provides answers to long-unanswered questions about the Sun and its solar flares.

"The place where all the energy is stored and released in solar flares has been invisible until now," said Gary.

"To play on a term from cosmology, it is the Sun's 'dark energy problem,' and previously we've had to infer indirectly that the flare's magnetic reconnection sheet existed," added Gary.

For solar physics, the measurements represent a better understanding of the Sun, as well as providing a path to revealing the truth behind the current sheet, and the magnetic bottle and its role in particle acceleration.

"There are certainly huge prospects out there for us to study that address these fundamental questions," said Shen.

The current study builds on the team's quantitative measurements of the evolving magnetic field strength directly follow a solar flare's ignition, published in Science earlier this year.