Gravitational microlensing is a method for discovering extra-solar planets. It is different to other techniques in that it is sensitive to planets in orbits around their host star where scientists think planets form most readily. In a recent work, Daisuke Suzuki of the Japan/New Zealand MOA collaboration announced that the most likely mass of such planets is about that of Neptune. The story was picked up by the New Zealand Herald today.

This graph plots 4,769 exoplanets and planet candidates according to their masses and relative distances from the snow line, the point where water and other materials freeze solid (vertical cyan line). Gravitational microlensing is particularly sensitive to planets in this region. Planets are shaded according to the discovery technique listed at right. Masses for unconfirmed planetary candidates from NASA’s Kepler mission are calculated based on their sizes. For comparison, the graph also includes the planets of our solar system.
Credit: NASA’s Goddard Space Flight Center

To reach this conclusion, Suzuki and his co-authors analysed a set of microlensing planets that have already been discovered, conducting a statistical analysis to infer the most likely planet mass of these cold planets. One of the planets included in the planet which I announced in Monthly Notices last year. The discovery and announcement of these planets power the sort of statistical analyses like that of the Suzuki et al result.

Neptune-mass exoplanets like the one shown in this artist’s rendering may be the most common in the icy regions of planetary systems. Beyond a certain distance from a young star, water and other substances remain frozen, leading to an abundant population of icy objects that can collide and form the cores of new planets. In the foreground, an icy body left over from this period drifts past the planet.
Credit: NASA’s Goddard Space Flight Center/Francis Reddy

Story: https://www.nasa.gov/feature/goddard/2016/most-common-outer-planets-likely-neptune-mass

Paper: http://iopscience.iop.org/article/10.3847/1538-4357/833/2/145

arXiv version of paper: http://adsabs.harvard.edu/abs/2016arXiv161203939S

Additional graphics: http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=12425

Video on YouTube: https://youtu.be/qzlR3kBCLYM

As Dr. Rattenbury has already mentioned in a previous post, the golden anniversary of the Mount John University Observatory (MJUO) was celebrated this year. I was fortunate to have been given the opportunity to attend and absorb the individual experiences of the astronomers.

The symposium’s theme centered around the observatory’s past, present and future. What I found most charming were the many stories told by astronomers who have become part of its history and who have had MJUO become an important part in their own lives in return.

Many times it felt like I was being transported to a cozy chair by a fireplace with grandpa recollecting the fascinating stories of his life, the adventures he had as an astronomer.

Here are only some of the many interesting things I heard during the symposium.

Audrey Walsh reflected upon her father, Frank Bateson’s work in establishing MJUO. Frank Bateson is the father of NZ astronomy, is has been said. In his own words, he was a “businessman by profession, astronomer by nature”. Hearing these words was an extremely inspiring moment for me, for it brings to my mind the image of a man who was passionate about his work.

Ed Guinan gave an entertaining account of the adventures and misadventures he had during the year he spent at MJUO and NZ in general. It was disheartening to hear that a chart of his results, which he kept close to him instead of shipping it, out of fear of losing it, was after all lost to the USSR customs while travelling through Russia.

The talk given by Alan Thomas painted a vivid picture of the contrast between observational astronomy as it was done all those years ago and how it is done now. Part of the excitement then was enduring the cold of the nights, snuggled up against a telescope in the open, in a sleeping bag, with a hot beverage, looking through the eye-piece.

Graeme Kershaw’s talk highlighted the fact that many countries have lost contact with the night sky so that lots of people come to lake Tekapo just to see the stars. He also pointed out the growing frustration of the elderly who grew up gazing up at the stars but can not offer the same to their children.

Many other talks painted similar pictures and drove it home that MJUO is one of the world’s most beautiful and easily accessible telescopes, rich with history and memories of individuals.

I have come out from this celebration with a refreshed aspiration for astronomy!

Annapolis is a pretty city, and played host to this year’s annual microlensing conference. Our host was Dr Rich Barry, Goddard Space Flight Centre.

There were a lot of interesting talks, planet discoveries and techniques being a primary focus, but with a strong influence coming from the proposed space telescope missions which may include microlensing observations in their additional science programmes.

There are two space telescope missions are ESA’s Euclid and NASA’s WFIRST/AFTA. Both are exciting missions. I contributed in a small way to the proposal to use Euclid for planetary microlensing. The last piece of work I did at Manchester was to write code to simulate microlensing observations, to estimate how many planets a space telescope could find, and of what type. I never finished that code, but it was taken over by Matthew Penny at Manchester as part of his PhD work, and he turned it into an excellent piece of software. Matt wrote an excellent paper on it.

It was great to catch up with Matt, and lots of other microlensers at the conference. Ashna Shara (my PhD student) was also there, to get to know the field, meet the people, and try to refine the topic of her PhD.

I gave a talk on — not microlensing — but on a piece of work that uses the large databases that the microlensing survey teams have accumulated. Next conference I hope to have something more on planetary microlensing!

The next international conference on microlensing will be held at NASA, Goddard Space Flight Centre in Annapolis!

There’ll be a long list of fascinating topics discussed. Here is a truncated list, filtered by my particular interests:

• Microlensing with Big data
• New discoveries in microlensing
• Data challenges – microlensing for the unwashed masses
• Planetary system formation history
• What could be derived directly from ground and space-based microlensing data sets – as is
• Space-borne ulensing missions
• WFIRST
• Euclid
• Ground-based microlensing in the era of WFIRST and Euclid
• Unbound planets
• Black holes, white dwarfs and other non-exoplanet lenses

http://asd.gsfc.nasa.gov/conferences/microlensing19/index.html

I am part of a group of astronomers advising NASA on what science the WFIRST space telescope could do. In particular, we think that the WFIRST mission could find extra-solar planets using microlensing. From our Report:

NASA’s proposed WFIRST-AFTA mission will discover thousands of exoplanets with separations from the habitable zone out to unbound planets, using the technique of gravitational microlensing. The Study Analysis Group 11 of the NASA Exoplanet Program Analysis Group was convened to explore scientific programs that can be undertaken now, and in the years leading up to WFIRST’s launch, in order to maximize the mission’s scientific return and to reduce technical and scientific risk. This report presents those findings, which include suggested precursor Hubble Space Telescope observations, a ground-based, NIR microlensing survey, and other programs to develop and deepen community scientific expertise prior to the mission.

Read the full report here.

Here is a Hollywood inspired trailer about WFIRST.

Exciting discovery of a planet in a microlensing event!

Here is TV One’s report.

Artist’s impression of the binary star system and the newly discovered planet. Adapted from image by Cheongho Han, Chungbuk National University, Korea.

Here is the University of Auckland’s press release:

Astronomers discover terrestrial planet in binary star system

New Zealand scientists are among an international team that has discovered an Earth-sized planet with an Earth-like orbit in a binary star system, the first terrestrial planet with an Earth-like orbit ever discovered in this commonly found star system.

Binary star systems are made up of two stars orbiting each other. Half the stars in our Galaxy are in binary systems.

The latest discovery expands astronomers’ understanding of where Earth-like planets can form and, potentially at least, whether or not they might be habitable.

The new planet is 3000 light years away and twice the mass of Earth. It orbits one of two stars in its binary system at about the same distance Earth orbits the Sun. But the star it orbits is much dimmer than our Sun, meaning the planet is extremely cold, around -210C, and unlikely to harbor life on its surface as we know it.

“This discovery is exciting because we weren’t certain that terrestrial planets could form around one star of a binary star system,” says University of Auckland Department of Physics senior lecturer Nicholas Rattenbury. “This tells us there are many more stars in our Galaxy that could potentially be the host star to habitable planets.”

New Zealand astronomers from Auckland, Massey and Canterbury universities contributed to this latest discovery along with amateur astronomers and staff at Auckland’s Stardome Observatory. The results are published today in Science with sixty-four authors named.

Scientists used a technique known as microlensing to detect the planet. Microlensing discovers planets by measuring how the gravity of a planet and its host star deflects light coming from background stars. By measuring how a background star appears to change brightness through the gravitational “lens” effect of the foreground star, astronomers can tell whether there is also a planet orbiting the foreground star.

Dr Rattenbury said working with such a big team of astronomers from around the world had been a thrill.

“Twenty years ago, the first extra-solar planet discoveries were being made. Today, we find it likely the Galaxy is teeming with planets. Will some of them harbour life? That is of course the big question.”

The research appears in the July 4th issue of Science:

A terrestrial planet in a ~1-AU orbit around one member of a ∼15-AU binary, A. Gould et al., Science, 4 July 2014: 46-49.