RASNZ Electronic Newsletter May 2016

The RASNZ Email newsletter is distributed by email on or near the 20th of each month. If you would like to be on the circulation list This email address is being protected from spambots. You need JavaScript enabled to view it. for a copy. The latest issue is below.

Email Newsletter Number 185

Affiliated Societies are welcome to reproduce any item in this email newsletter or on the RASNZ website http://www.rasnz.org.nz/in their own newsletters provided an acknowledgement of the source is also included.

Contents

1. Executive Secretary Sought
2. Affiliated Societies' Committee Meeting Agenda
3. Annual General Meeting Agenda
4. The Solar System in June
5. Royal Society of NZ 150th Celebration
6. VSS Symposium 4 Report
7. Extra-Bright Supernova Re-brightens!
8. Milky Way's Nuclear Star Cluster Imaged
9. More Kepler Planets Confirmed
10. Young Planetary System Imaged
11. Saturn's Moons New?
12. How to Join the RASNZ
13. Quotes

1. Executive Secretary Sought

Want to make a difference? RASNZ is looking for a new Executive Secretary. This council position involves doing the administrative tasks of the society, minutes, email, letters etc., but also provides an opportunity to contribute to the direction and activities of the RASNZ. You will need 20 minutes a day to deal with email and other correspondence, more time around the annual conference to complete reports and admin tasks. Access to a word processing and spreadsheet programs are needed. If you think you can fill this significant role for RASNZ then contact John Drummond This email address is being protected from spambots. You need JavaScript enabled to view it.. For more detailed information on the job details contact the current secretary at This email address is being protected from spambots. You need JavaScript enabled to view it.

2. Affiliated Societies' Committee Meeting Agenda

THE 2016 RASNZ AFFILIATED SOCIETIES´ COMMITTEE MEETING AGENDA Affiliated Societies Committee Meeting 2016 - Friday 20 May 2016 at the Quality Inn, Napier commencing at about 4:30 p.m.

Agenda: 1) Apologies. 2) Minutes of the previous affiliated societies committee meeting held at Tekapo 3) Matters arising from the minutes. 4) Election of Affiliated Societies Representatives to Council 2016- 2018 5) General business a) Insurance and Health and Safety - Bob Evans

If there are any items which a Society wishes to have raised in General Business, please send them ASAP to the Executive Secretary at the address below. The minutes of the 2015 affiliated societies committee meeting have been placed on the RASNZ web site at http://www.rasnz.org.nz/affsoc-minutes. Please send communications about this agenda to me by email at This email address is being protected from spambots. You need JavaScript enabled to view it. or post to 662 Onewhero-Tuakau Bridge Rd, RD 2, TUAKAU 2697.

At the Meeting in 2006, it was resolved that the committee should consist of the presidents/chairs of societies or their appointed deputies. Please inform me if the president of your society is unable to attend, and who the appointed deputy may be. If your society will not be represented, an apology would be appreciated.

Rory O´Keeffe, Executive Secretary, May 2016 ----------

Remember to visit our Affiliated Societies page - http://rasnz.org.nz/rasnz/affiliated-societies-details

-- Copied from Keeping in Touch #16 - 14th May 2016, circulated by John Drummond, RASNZ vice-president. Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

3. Annual General Meeting Agenda

THE 93rd (2016) RASNZ ANNUAL GENERAL MEETING AGENDA 93rd Annual General Meeting - Sat 21 May 2016, MTG Hawkes Bay, 1 Tennyson St, Napier, at 4.30 pm.

Agenda

1. Apologies

2. Respect for Deceased Members 3. Greetings to Absent Members. 4. Minutes of the 92nd AGM held in Tekapo. 5. Matters arising from the Minutes. 6. Annual report of council for 2015 7. Annual accounts for 2015 8. Election of Officers and Council for 2016-2018 The following nominations have been received: Position Nominee Proposed Seconded President John Drummond Gordon Hudson Murray Forbes Vice President Nick Rattenbury Simon Lowther John Hearnshaw Treasurer Simon Lowther Rory O´Keeffe John Hearnshaw Fellows´ Rep Karen Pollard Bob Evans John Hearnshaw Councillors Bob Evans Pauline Loader Brian Loader Steve Butler Rory O´Keeffe John Hearnshaw Glen Rowe Warwick Kissling Gordon Hudson Sergei Gulyaev John Hearnshaw Grant Christie Orlon Petterson Karen Pollard John Hearnshaw

John Hearnshaw, as President 2014-2016, will be on council ex-officio as a Vice President. There was no nomination for Secretary. Nominations may be taken from the floor of the AGM for Secretary. As the number of nominations did not exceed the positions available, no election was necessary. Affiliated Societies´ Reps are elected at the Affiliated Societies Committee meeting (Fri 20 May).

  1. Election of Auditor.
  2. Election of Honorary Solicitor.
  3. Election of a new Fellow of the Society
  4. Election of an Honorary Member of the Society
  5. General Business as allowed for in the rules.

Yours sincerely, Rory O´Keeffe, Executive Secretary, May 2016

-- Copied from Keeping in Touch #16 - 14th May 2016 circulated by John Drummond, RASNZ vice-president. Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

4. The Solar System in June

Dates and times shown are NZST (UT + 12 hours) unless otherwise stated.

Rise and set times are for Wellington. They will vary by a few minutes elsewhere in NZ.

The southern hemisphere winter solstice is on June 21 with the Sun furthest north at about 10am.

Sunrise, sunset and twilight times in june

                            June  1  NZST                    June 30  NZST
              morning        evening         morning        evening
SUN:         rise: 7.34am,  set: 5.02pm     rise: 7.45am,  set: 5.04pm
Twilights
 Civil:    starts: 7.06am, ends: 5.31pm   starts: 7.16am, ends: 5.33pm
 Nautical: starts: 6.32am, ends: 6.05pm   starts: 6.42am, ends: 6.07pm
 Astro:    starts: 5.58am, ends: 6.39pm   starts: 6.08am, ends: 6.41pm

June phases of the moon (times as shown by guide)

          New moon:      June  5 at  3.00 pm (03:00 UT)
  First quarter: June 12 at  8.10 pm (08:12 UT)
  Full moon:     June 20 at 11.02 pm (11:02 UT)
  Last quarter   June 28 at  6.19 am (June 27, 18:19 UT)

The planets in June

Mars, Saturn and Jupiter will be prominent in the evening sky with the latter low by late evening. Mercury will start June as an easy morning object in the dawn sky. It will brighten during the month but get too close to the Sun to observe towards the end of June.

Venus is at superior conjunction on June 7, it then becomes an evening object but remains too close to the Sun to observe.

MERCURY starts June as a morning object rising more than 2 hours before the Sun on the 1st. With a magnitude 0.9 it will be 10° up an hour before sunrise. Look for Mercury in a direction nearly 30° north of east. The planet is at its greatest elongation 24° west of the Sun on the 5th. During the rest of June Mercury will slip back towards the Sun but also gain in brightness, reaching a magnitude -1.6 on the 30th. But by then it will rise only 30 minutes before the Sun.

On the morning of June 4 a very thin crescent moon will be 6° from Mercury, the moon to the lower right of the planet. An occultation of Mercury by the moon, shortly before midnight NZ time, will only be visible from parts of the southern Atlantic Ocean including South Georgia.

VENUS is close to the Sun all month. Too close for observation. On the first it rises into the morning sky only 7 minutes before the Sun.

The planet is at superior conjunction on the far side of the Sun on June 7. At this conjunction Venus will pass behind the Sun as "seen" from the Earth. In fact the "occultation" of Venus by the Sun lasts from about 11 am on June 6 (June 5, 23hr UT) to 9am on June 8 (June 7, 21 hr UT), that is for some 46 hours. At conjunction Venus will be 108 million km (0.72 au) beyond the Sun

After conjunction Venus will become an evening object. By the end of June it will set only 25 minutes after the Sun.

MARS starts June at magnitude -2.0, the same as Jupiter. But the colours are very different, Mars being distinctly orange. Following conjunction late in May, the Earth will be pulling away from Mars during June. As a result the planet will dim a little, but still be at magnitude -1.6 on the 30th.

During June Mars will be in Libra moving to the west towards alpha Lib and away from Antares and Saturn. The planet is stationary on June 30.

The 90% lit moon will be at its closest to Mars for the month on the evening of the 17th when the two will be a little over 8° apart..

JUPITER will be best placed for viewing early evening as it sets shortly after midnight on the 1st and at 10.42 pm on the 30th. The planet remains in Leo, its position changes little during the month, being stationary on June 10.

The 41% lit moon will be about 5° below Jupiter an hour or so before they set on June 11. They will be considerably closer, while below NZ's horizon, a few hours later.

SATURN is at opposition on June 3, so will be rising close to the time of sunset and setting near the time the Sun rises. At opposition Saturn will be 1.35 billion km from the Earth (9.01 AU) and a further 150 million km from the Sun.

The planet is in Ophiuchus moving slowly to the west a few degrees below Antares, as seen in the evening. With a zero magnitude Saturn is noticeably brighter than Antares or any other star near it. Mars, brighter still, is 18° from Saturn.

The moon passes Saturn on the 19th but the two will be closest soon after midday. By the time they are visible in the evening the almost full moon will be 5° below Saturn. The latter will be about 22° up to the east.

Outer planets

URANUS is a morning object in Pisces at magnitude 5.9. It rises about 4 hours before the Sun on June 1 and 6 hours earlier on the 30th. The moon passes Uranus twice during June.

On the morning of June 2 at about 7am, the 15% lit crescent moon will be just over 3° from Uranus. The planet will be to the left of the moon and a little higher. It should be easy to spot Uranus using binoculars, there are two stars a little fainter than Uranus between the two.

The moon passes Uranus again on the 29th. This time the two are closest at midday, at 7am they will again be just over 3° apart, with the 38% lit moon above and a little to the left of Uranus..

NEPTUNE rises at midnight on June 1 and nearly 2 hours earlier on the 30th. So the planet is beginning to move into the evening sky, but will still be best placed for viewing in the morning a while before sunrise. The planet, at magnitude 7.9, is in Aquarius.

Neptune is stationary on June 14 after which it will start to move slowly to the west. It will be about half a degree from the 3.7 magnitude star lambda Aqr. The planet will be to the upper right of the star. No stars as bright as Neptune are between the two.

PLUTO at magnitude 14.3 rises early evening during June, less than half an hour after sunset by the end of the month. The planet remains in Sagittarius. It passes the 2.9 magnitude star pi Sgr during June, with the two only 3 arc-minutes apart, one-tenth the diameter of the full moon, on the 25th.

Minor planets

(1) Ceres, magnitude 9.3, is in Cetus during June. It rises at 2.45 am on the 1st and just under an hour earlier by the 31st.

(4) Vesta is a dawn object in Taurus. At the beginning of June it rises half an hour before the Sun, by the end of the month some 95 minutes before the Sun. Mercury passes Vesta during June as the two move east. They are closest on the mornings of June 22 and 23 when Vesta (magnitude 8.4) will be 2° to the upper right of Mercury (magnitude -0.8)

-- Brian Loader

5. Royal Society of NZ 150th Celebration

The RASNZ received the following note from the Royal Society of NZ.

The Royal Society of New Zealand celebrates our 150th birthday in 2017.  
Over 150 years we have worked to promote new knowledge, and now work 
towards a New Zealand enriched by science, technology and humanities.  
As constituent organisations you are of course independent, but if you 
would like to join us in recognising our 150th anniversary, we have a 
suggestion. Our President or Vice Presidents are available to give a 
short talk and show a short video at one of your events between April 
and October 2017. In this way we can celebrate the partnerships we have 
had past and present and look to the future. We will be highlighting 
our multi-disciplinary focus, celebrating success and looking to the 
future. We would be interested to know if this is an attractive option 
for your organisation.

-- Dr Andrew Cleland, Chief Executive. www.royalsociety.org.nz

6. VSS Symposium 4 Report

The latest issue (April 2016) of the Variable Star South newsletter is available on the website: Here is the link: www.variablestarssouth.org/latestnewsletter

There is an article in the Newsletter by the Editor Phil Evans about the VSS Symposium 4 held recently in Sydney. It gives a short account of each of the presentations, so you can get an idea of the main ideas presented in a short read; refer to pages 16 to 20 of the Newsletter. As well as this overview there are the following articles based on presentations at the Symposium:

Ed Budding Deciphering the Enigma of QZ Carinae ((refer pg 20) Jeff Byron A toolbox for eclipsing binary stage 1 analysis (pg 26) Murray Forbes An improved method for correcting atmospheric extinction (pg 34)

To follow up on any of the techniques mentioned at the Symposium refer to the Research Tabs of the website or email the Research Coordinator.

-- Alan Baldwin

7. Extra-Bright Supernova Re-brightens!

Subo Dong (Peking University, China) and colleagues discovered the powerful stellar explosion known as ASASSN-15lh on June 14, 2015, using the All-Sky Automated Survey for Supernovae (ASASSN). [See Newsletter No. 183, Item 8.] Four robotic 14-centimeter telescopes, collectively known as Cassius and stationed at Cerro Tololo, Chile, were staring at the entire visible sky when they spotted the flash. Since then, the supernova has baffled astronomers.

The typical supernova goes something like this: a star ages, burning up its core´s hydrogen, then helium, and so on up the element chain until it reaches iron, when fusion stops. At that point, the core can no longer support itself against the inward crush of gravity. The star´s outer layers rush inward too, but they bounce off the collapsed core and energy from the collapse throws them back out in a brilliant flash.

The light from ASASSN-15lh took almost 3 billion years to arrive at Earth, its extreme distance muting the visible brilliance to a mere 17th magnitude. Nevertheless, its peak power was more than twice that of any previously known stellar explosion. Usually, much of a supernova´s initial glow actually comes from radioactive nickel, created in abundance near the core. What´s weird about ASASSN-15lh (and a few others like it) is that they´re so bright, they´d need an awful lot of nickel to explain their glow.

Of course, ASASSN-15lh faded, as supernovae are wont to do. But this particular supernova held a surprise for researchers. Roughly three months after it began dimming, the supernova changed course. For 40- some days, its ultraviolet radiation charged up, increasing fivefold before plateauing for another couple of months and finally dropping away again. Radiation at visible wavelengths ignored this transformation and continued to fade unabated.

A born-again supernova isn´t unheard of. But typically when that happens, the blast has run into nearby gas that the star threw out before it exploded. ASASSN-15lh doesn´t display any of the emission lines you´d expect in its spectra if this were the case.

Until now, the most successful explanation of ASASSN-15lh´s oddities has been the magnetar. In this scenario, the core of an aging, massive star collapsed to form a spinning stellar remnant that´s like a neutron star but with a magnetic field at least 100 billion times the strength of the Sun´s strongest fields. Rather than radioactive elements, the supernova´s power would come from the magnetar´s gyrating magnetic field.

But as magnetars go, this one has to be pretty weird: to produce the radiation initially seen from ASASSN-15lh, the magnetar would have had to convert almost all its magnetic and rotational energy to radiation. Now, factoring in the extra energy recently emitted in the ultraviolet makes the demands on the magnetar model even more stringent. "The magnetar model is safe, but barely," says Todd Thompson (Ohio State University). "The magnetar [scenario] would be in danger if we saw roughly two times more energy. It would begin to push what we think is possible. "Of course," Thompson adds, "without another viable alternative, we might still try to make the magnetar model work."

Not everybody agrees: Peter Brown (Texas A&M University) just posted another paper on the topic on the arXiv's astrophysics preprint server. Brown and colleagues argue that while the magnetar scenario might provide a good explanation of the initial ASASSN-15lh observations, it doesn't suffice to explain the object's resurgence at ultraviolet wavelengths. Whatever ASASSN-15lh may be, one thing's for sure - the exceptional object isn't lending itself to any easy explanations.

-- Abridged from the article by Monica Young on Sky & Telescope's webpage. See the original with graphs and graphics at http://www.skyandtelescope.com/astronomy-news/the-resurgence-of-the-brightest-supernova/#sthash.H2ciXOn2.dpuf

8. Milky Way's Nuclear Star Cluster Imaged

Peering deep into the heart of our home galaxy, the Milky Way, the NASA/ESA Hubble Space Telescope has imaged the half a million stars that are members of the Milky Way's nuclear star cluster. This is the densest and most massive star cluster in the galaxy.

The centre of the Milky Way, 27 000 light-years away in the constellation of Sagittarius, is a crowded place. This region is so tightly packed that it is equivalent to having one million stars crammed into the volume of space between us and Alpha Centauri, located 4.3 light-years away. At the very hub of our galaxy, this dense nuclear star cluster surrounds the Milky Way's central supermassive black hole, known as Sagittarius A*, which alone is about four million times the mass of the Sun.

Sagittarius A* is not the only mystery lurking in this part of the galaxy. The crowded centre contains numerous objects that are hidden at visible wavelengths by thick clouds of dust in the galaxy's disc. In order to truly understand the central part of our galaxy astronomers used the infrared vision of Hubble to peer through this obscuring dust. To reveal the image in all its glory the scientists then assigned visible colours to the different wavelengths of infrared light, which is invisible to human eyes. It is estimated that there are about 10 million stars in the cluster which are too faint to see, even for Hubble.

Using Hubble's vantage point above the atmosphere and its high resolution, astronomers were also able to measure the movements of the stars over a period of four years. Using this information, they inferred important properties of the nuclear star cluster, such as its mass and structure. The motion of the stars may also offer astronomers a glimpse into how the nuclear star cluster was formed - whether it was built up over time from globular star clusters that happened to fall into the centre of the galaxy, or from gas spiralling in from the Milky Way's disc to form stars at the core.

See the image and full text at http://hubblesite.org/newscenter/archive/releases/2016/11/

-- from a NASA/ESA press release forwarded by Karen Pollard. ----------

For more images and notes that there hasn't been space for recently, see: http://www.eso.org/public/images/eso1547a/

http://hubblesite.org/newscenter/archive/releases/2007/08/image/a/
http://www.eso.org/public/images/eso1605a/
https://www.eso.org/public/images/archive/top100/
http://subarutelescope.org/Pressrelease/2016/02/03/index.html
http://www.eso.org/public/archives/images/original/eso1547a.tif

9. More Kepler Planets Confirmed

Even though Kepler´s primary mission ended three years ago, the data it collected just revealed a mother lode: 1,284 newly confirmed planets.

Over the course of four years, the Kepler spacecraft stared at a tiny patch of sky teeming with stars and tallied up 4,696 exoplanet candidates. But for years now, many have remained just that: candidates. To confirm any one planet requires difficult, time- consuming follow-up observations. And the smaller candidates are out of reach of even the largest ground-based telescopes. After years of follow-up observations, the list of confirmed planets stood at 1,041 - nothing to sneeze at, but nowhere near complete Now that list has just doubled in size. With the newest study from the Kepler team, the confirmed planets now number 2,325 Timothy Morton (Princeton University) and colleagues accomplished that feat by taking a different tack than their predecessors.

Acknowledging that follow-up observations wouldn´t be possible for all planet candidates, the team didn´t look for additional evidence supporting a planet´s existence. Instead, they searched for signs that the planet wasn´t there. Then they calculated the chance that what looked like a planet was actually an imposter. Any candidate with less than a 1% chance of being fake is now considered real.

When astronomers look for transiting planets, they never actually see the planet itself. Instead they see a dip in the host star´s light as the planet passes in front of it. But other astrophysical sources can mimic that dip. The most common imposter is an edge-on pair of stars whose mutual orbit blinks on and off in the background - an eclipsing binary.

Morton and his team took a two-pronged, fully automated approach to determining whether a signal was an imposter or a real planet. Their code first examined the signal itself - a real planet transit will block the star´s light in a certain way that can sometimes be distinguished from imposters. Then the code factored in how common imposters might be. For example, how common are binary stars, and how many lie in the direction Kepler was looking?

The algorithm studied each planet candidate for several minutes, then spit out a probability that the signal is a fake. And as long as that probability was less than 1%, the candidate moved to the confirmed list.

All in all, 1,935 planets were confirmed in this way, including 651 that had already been confirmed by some other method. And 428 candidates (generally those with large radii, whose signals are more easily faked by other astrophysical sources) were flagged as imposters.

Several thousand candidates remain in limbo, not quite flagrant enough to be flagged as fakes, but not quite convincing enough to be confirmed either. These candidates await improvements to Morton´s algorithm, follow-up observations, or both. Of the newly confirmed planets, nine orbit in their star´s habitable zone, the region in which a planet with an Earth-like atmosphere could sustain liquid water on its surface. Add that to the dozen already known, and astronomers have assembled a decent size of potentially habitable planets.

The Kepler mission will close out in a year and a half, says mission scientist Natalie Batalha (NASA Ames), though we can expect one last Kepler catalogue sometime next year. The secondary K2 mission is still going strong and will likely end in mid-2018, when the spacecraft runs out of fuel.

"We´re getting ready to pass the baton to future missions," Batalha adds, namely, the dynamic duo: the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST).

10. Young Planetary System Imaged

A new image from the Atacama Large Millimetre/submillimetre Array (ALMA) shows the finest detail ever seen in the planet-forming disc around the nearby Sun-like star TW Hydrae. It reveals a tantalising gap at the same distance from the star as the Earth is from the Sun, which may mean that an infant version of our home planet, or possibly a more massive super-Earth, is beginning to form there.

The star TW Hydrae is a popular target of study for astronomers because of its proximity to Earth (only about 175 light-years away) and its status as an infant star (about 10 million years old). It also has a face-on orientation as seen from Earth. This gives astronomers a rare, undistorted view of the complete protoplanetary disc around the star.

Other pronounced gaps that show up in the new images are located three billion and six billion kilometres from the central star, similar to the average distances from the Sun to Uranus and Pluto in the Solar System. They too are likely to be the results of particles that came together to form planets, which then swept their orbits clear of dust and gas and shepherded the remaining material into well-defined bands.

For the new TW Hydrae observations, astronomers imaged the faint radio emission from millimetre-sized dust grains in the disc, revealing details on the order of the distance between the Earth and the Sun (about 150 million km). These detailed observations were made possible with ALMA's high-resolution, long-baseline configuration. When ALMA's dishes are at their maximum separation, up to 15 kilometres apart, the telescope is able to resolve finer details.

Earlier ALMA observations of another system, HL Tauri, show that even younger protoplanetary discs - a mere 1 million years old - can display similar signatures of planet formation. By studying the older TW Hydrae disc, astronomers hope to better understand the evolution of our own planet and the prospects for similar systems throughout the Milky Way.

The astronomers now want to find out how common these kinds of features are in discs around other young stars and how they might change with time or environment.

See the ALMA images at http://www.eso.org/public/images/?search=eso1611 The resulting paper is at http://www.eso.org/public/archives/releases/sciencepapers/eso1611/eso1611a.pdf

-- From a press release forwarded by Karen Pollard.

11. Saturn's Moons New?

Though Saturn has 62 moons (to date) only Titan is of significant size. With a diameter of 5151 km it is the second biggest moon in the Solar System after Ganymede. Its mass is nearly twice that of our Moon, giving it enough gravity to retain a dense atmosphere with liquids forming lakes.

Curiously, though, Saturn's other moons are small alongside Titan. Their sizes ranging from Mimas´s 400 km to Rhea´s 1,525 km. Together, they have a mere twentieth as much mass as Titan does. Interspersed with these are a vast collection of moonlets, with sizes of a few tens to a couple hundred km. Some of these are likely born from pileups of ring material.

In terms of numbers, Saturn´s retinue matches that of the king of the planets, Jupiter, whose current satellite tally also happens to be 62. But Jupiter's moons are much bigger with its four Galilean moons (some of the largest moons in the solar system), two of which are comparable in size to Mercury. Titan´s elongated orbit and loner status set it apart from this stately satellite quartet. And Jupiter doesn´t have any mid-size moons.

Planetary scientists have long wondered why Jupiter has come out so much the winner when it comes to big moons. In 2013, for example, Erik Asphaug (Arizona State University) and Andreas Reufer (then at University of Bern, Switzerland) suggested that Saturn started with a Galilean system of its own, but the moons crashed into and obliterated one another. The rubble then coalesced into Titan and the mid-size moons.

A new paper explores this collision idea further. Matija Cuk (SETI Institute) and his colleagues turned back time by studying the icy moons´ motions and figuring out when and how they could have interacted, given their current orbits. Some moons move in what are called orbital resonances, which means the time it takes Moon A to complete an orbit around Saturn is a simple fraction (say, one half) of the time it takes Moon B to do so. Resonant moons strongly affect each other´s orbits, easily tilting them out of the original plane in which they lay.

Saturn also has an off-putting effect on its satellites, pushing them farther away with time. This tidal push is strong because the planet isn´t solid. It affects each of the various moons in different ways, changing each of their orbits with time and making and breaking resonances.

What the team found was that, given the moons´ current (and backtracked) orbits, the moons can´t have migrated much from where they first formed. But that doesn´t make sense if they´ve been orbiting the planet from the solar system´s early days: Saturn´s tides are just too tenacious - the moon Enceladus and its tidal-triggered geysers confirm that.

Instead, the team argues, the mid-size moons can only be about 100 million years old - or, as the SETI Institute´s press release puts it, "younger than the dinosaurs." (Dinosaurs first appeared in the Triassic period, 230 million years ago.) The moons formed from a ring of debris, born from the collisions of a previous population of moons, the team suggests in the April 1st Astrophysical Journal.

That´s consistent with his Galilean squabble theory, Asphaug says. Unlike Asphaug and Reufer, Cuk´s team doesn´t argue in favour of Titan being a merger-born moon, but that suggestion "definitely ranks as hypothetical," Asphaug readily admits.

Cuk´s team offers a test: craters. If the mid-size moons are indeed young, they won´t have had time to build up a perfectly homogenous peppering of pockmarks from space. Instead, craters on moons within Titan´s orbit (all the mid-size moons but Iapetus) would concentrate around those satellites´ equators, because the moons would have been exposed to a lot of debris in the plane of their birth ring but not nearly as much from other angles. Many of the moons are heavily scarred, so it´ll take dedicated work to tease out whether the moons have these girdles.

References: 1. Cuk et al. "Dynamical Evidence for a Late Formation of Saturn´s Moons." Astrophysical Journal, vol. 820, no. 2 (April 1, 2016). 2. Asphaug and A. Reufer. "Late Origin of the Saturn System." Icarus, vol 223, issue 1 (March 2013).

-- Abridged from an article by Camille M. Carlisle of 15 April on Sky & Telescope's website.

12. How to Join the RASNZ

RASNZ membership is open to all individuals with an interest in astronomy in New Zealand. Information about the society and its objects can be found at http://rasnz.org.nz/rasnz/membership-benefits A membership form can be either obtained from This email address is being protected from spambots. You need JavaScript enabled to view it. or by completing the online application form found at http://rasnz.org.nz/rasnz/membership-application Basic membership for the 2016 year starts at $40 for an ordinary member, which includes an electronic subscription to our journal 'Southern Stars'.

13. Quotes

"But there's kind of a notion that 'everyone's opinion is equally valid.' My arse! A bloke who's a professor of dentistry for 40 years does not have to debate with some idiot who removes his teeth with a string and a door!" -- Dara O'Briain.

"Sceptical scrutiny is the means, in both science and religion, by which deep insights can be winnowed from deep nonsense." -- Carl Sagan.

"When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others." -- Bertrand Russell.

Newsletter editor:

Alan Gilmore Phone: 03 680 6817
P.O. Box 57 Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
Lake Tekapo 7945
New Zealand