Monthly Archives: September 2018

“There are more Exoplanets than stars in our galaxy”

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How many stars are there in our own galaxy, the Milky Way? A number frequently bandied about is 100 billion. This is a nice round number. The number could be as high as 400 billion; also a nice round number. In an interesting coincidence, the number of galaxies is estimated at 100 billion, a number that will no doubt increase as we peer into the farthest recesses of the universe. So, a 100 billion galaxies, and in each 100-400 billion stars – the numbers are getting out of hand (even for a geologist who works in millions of years).

So when astronomers announce that there are probably more exoplanets than stars in our own galaxy (ergo all the other galaxies), our ego-centric view of the universe seems just plain silly.  As of September 25, 2018, there were 3779 confirmed planets, 2737 NASA candidates, and 2819 solar systems. The graph below shows the astonishing rate of discovery over the last two decades; 2016 was a banner year with almost 1500 identifications. The NASA plot shows the estimated planet size and orbital periods, relative to Earth; the majority of exoplanets apparently whiz round their stars in less than 100 days, some in a few hours.

So, how does one discover a new exoplanet?

Having a decent telescope at your disposal is a good start. Land-based telescopes are okay, but the real successes have been with orbiting, satellite-based telescopes. Kepler was launched by NASA in March 2009 and was tasked with watching a swath of sky containing about 150,000 sun-like stars. About 70% of the discoveries so far have been made by Kepler. The second orbiting observatory, TESS (Transiting Exoplanet Survey Satellite), launched April 18, 2018, is also dedicated to finding exoplanets, and in its first few days of operation has made some exciting discoveries.

Kepler and TESS use a method of detection called Transiting – several other methods have been used but the transit method has been the most successful (e.g. Radial Velocity measures apparent changes in the velocity of a star’s own motion, or wobble, caused by the orbiting planet. An observer will see velocity changing as the star move towards and away from Earth. A nice summary of detection methods has been compiled by The Planetary Society). A transit occurs when a planet passes between its star and an observer on (or orbiting) Earth.  The planetary disc will block some of the star’s light, and if the telescope is pointing in the right direction, the reduction in luminosity can be measured. Planetary orbits are periodic. Therefore, an important part of the analysis is observing dimming at regular intervals.

Astronomer Edmund Halley (of Halley’s comet fame), and Captain James Cook provide us with a useful historical analogy. Halley surmised that observations of Venus during its transit of the Sun, from different geographical locations, would permit calculations of astronomical distances, and hence, the size of the solar system (the calculations involved simple trigonometry). Cook was dispatched to Tahiti in time for the June 4, 1769 transit. The disc presented by Venus is small compared to the Sun, but there is a measurable decrease in light during its transit.

A more dramatic example of a transit occurs in our own backyard, when the Moon passes between the Sun and Earth during daylight hours. Partial eclipses produce observable dimming of sunlight, but a full eclipse delivers brief twilight. This principle also applies to exoplanets.

In its first few days of operation, TESS discovered a planet orbiting the star Pi Mensae, a bright dwarf star about 60 light years from Earth. The observed period of starlight dimming indicates that Pi Mensae c has an orbit of only 6.27 days. But what about its size – its radius and mass compared to Earth?

Astronomers start by measuring the size of the star; this they can do quite accurately because stars are fairly predictable. The brighter a star, the hotter it burns. Thus, the colour spectrum emitted provides a good indication of its temperature. Knowing the brightness and temperature it is then possible to calculate the surface area of the star (the larger the surface area, the more light it will emit), and if surface area is known, simple arithmetic will give you the star’s diameter.

During a planet’s transit, a measurable proportion of star light will be dimmed – in other words, the planet will dim the light in proportion to its size. Bingo! We now know the size (radius) of our exoplanet. But we still need to know how ‘heavy’ it is.

This is determined by observing the gravitational tug of war between the planet and its sun. The orbiting exoplanet will cause its sun to wobble about its axis; the degree of wobbling will be proportional to the exoplanet mass (we already know the star’s mass).  These very small gravitational perturbations can be measured by Kepler, TESS, and earth-based telescopes.

Knowing the exoplanet size and mass, gives us all the information we need to calculate its density.  Newly discovered Pi Mensae-c has a radius 2.14 times, and a mass 4.82 times that of Earth. So it is roughly Earth-size, but too close to its sun to be habitable.

The Transit method is not without its drawbacks. Importantly, the exoplanet orbit must be aligned with the observer. There must be as many orbit geometries as there are planetary systems in our galaxy, which means our telescopes can detect only a fraction of all possible exoplanets. Binary stars (i.e. two stars in very close proximity having mutual orbits) can also complicate observations of transit and gravitational wobbles. Celestial bodies the size of Jupiter can also be problematic because this size range can include some dwarf stars.

I don’t know about you, but it seems that new discoveries or exploration events are announced almost on a daily basis. Some of the latest excitement centers on two small robots that are playing leap frog on asteroid Ryugu. The number of questions seems to expand exponentially, the more we delve into our universe. Exoplanet science will go a long way to answering some of the questions.

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Bluebottle entanglements; or how to ruin your day at the beach

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The southern hemisphere is coming into summer; it’s done this every year for as long as I can remember. For New Zealanders, and pretty well anyone else in this ocean-locked world there is an exodus, a migration as the population ups-sticks and heads to the beach. Unlike our nearest neighbour, we are not thwarted by crocs, sea snakes, Stone Fish or Box Jellyfish; Great Whites mostly ignore us. From the point of view of dastardly critters, these shores would be considered benign. Except for Bluebottles.

Bluebottles galore; entanglements that can ruin a perfect day at the beach (soft, squishy and potentially dangerous).  There are thousands of Bluebottle stings reported every year in New Zealand and Australia. Bluebottles are related to jellyfish, a very pretty blue, puffed up balloon-like, stranded along the high tide line, bedraggled. These creatures, delicately laced, frequently litter NZ beaches (and elsewhere), blown ashore on the tide.

Bluebottles belong to a group of marine animals (a phylum) called Cnidarians, a group that includes corals, sea anemones, true jellyfish, and siphonophores. They all have stinging cells (nematocysts), although corals, sea anenomes and many jellyfish tend to be relatively benign – except to the small critters they like to eat.

Bluebottles are not Jellyfish, they are siphonophores. A true Jellyfish is a single organism, a medusa that possesses a central gut and nervous system; they are all free swimming (Sea Anemones also are single organisms, consisting of a polyp attached to rock, shell or sediment).  Bluebottles are colonial organisms containing a myriad, microscopic, multicellular animals, or zooids, that find solace in community living. Despite being individuals, zooids are attached to and dependent on each other. Zooids tend to have specialized functions; some are attuned to digestion, others to swimming or carrying nematocysts in the tentacles .

The two most common species are Bluebottles that inhabit the Pacific and Indian oceans (the species Physalia utriculus), and the Atlantic (Physalia physalis), the latter more commonly known as the Portuguese Man o’ War (see image at the top of this post).  Both have an easily identifiable gas-filled bladder (pneumatophore) in an attractive blue with hints of mauve, from which dangle tentacles – the things do the damage to passing small fish and people. The bladders provide the only means for movement by catching wind and waves (again, unlike Jellyfish that propel themselves).

Portuguese Men o’ War tend to be larger than their Pacific cousins, with tentacles extending 10m, and even 30m below the sea surface.  Bluebottles have smaller pneumatophores, and fewer and shorter tentacles. The tentacles contain many stinging cells called nematocysts; their sole function is to catch and stun prey. Nematocysts on Bluebottles and Portuguese Men of War can penetrate skin to inject venom. A single stinging cell will do little damage. Unfortunately, tentacles tend to wrap their prey (including arms and legs), in an act of evolutionary hubris that inflicts multiple stings manifested in a nicely symmetrical, cork-screw like pattern of welts.

Bluebottle stings are painful- I can attest to this. In most people, this is as far as it goes, but if you are unfortunate to have tentacles wrapped around large areas of your semi-naked body, the venom can induce nausea and headaches, and in more serious cases, difficulty breathing or cardiovascular failure (happily the latter are rare).

There is plenty of advice on how to deal with Bluebottle and Portuguese Man o’ War stings. First and foremost, don’t try to rub or scrape off the tentacles; this will only exacerbate envenomation. Use seawater to wash thoroughly the affected area. Some authorities recommend dabbing vinegar on the welts to help ease the pain; others suggest this only makes matters worse (this link is an Open Access document). I must admit, a bottle of vinegar is not usually on my list of things to take to the beach, unless I’m planning to cook shellfish.

There is also the mistaken belief that peeing on the affected area will help. Urinating on oneself might be awkward, so you would probably need a willing accomplice.  But the real kicker here is that pee makes the nematocysts release more venom. So, if anyone suggests this remedy, do let them know it is nonsensical, notwithstanding the public spectacle. Tentacles can also release venom long after they have been blown ashore.  So it’s best to admire them from a distance.

Enjoy summer.

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Atlas of the Burrens, County Clare

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Here’s a selection of photos from the Burrens of County Clare, Ireland. Carboniferous limestones, in a glacio-karst landscape: karst structures, landscapes, vegetation, and fossils, from inland and shoreline exposures.

There is an article on the Burrens here.

The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source as indicated below (it is the polite, and professional thing to do).  I retain copyright of all images presented herein; there are a few exception and these are indicated in the captions as image credit.

Brian Ricketts –  www.geological-digressions.com

This link will take you to an explanation of the Atlas series, the ownership, use and acknowledgment of images.  There, you will also find links to the other Atlas categories.

Click on the image for an expanded view, then ‘back page’ arrow to return to the Atlas.

New Quay and Abott Hill:

  

Burrens landscape north of Boston (a few km south of New Quay. Limited soil cover on the limestone bedrock, and scrubby vegetation. Typical rounded hills of limestone in the background.

 

Views north of the estuary and Galway Bay from Abott Hill (between New Quay and Kinvara)

 

Clints and grykes, Abott Hill, typical Burren karst structures.  Right image: smaller scale dissolution rills.

 

Typical Burren hill and more fertile lowland valley near New Quay

 

Flaggy Shore (near New Quay):

Salt corrosion and erosion of limestone along Flaggy Shore, has modified the clints and grykes. Some erosion is caused by potholed cobbles.

 

Clints and grykes on the raised shore platform along Flaggy Shore

 

Abundant colonial Visean corals, best seen on semi-polished surfaces along the Shore. These views are oblique and cross-sections of coral columns.

 

Black Head:

The raised shore platform at Black Head (below the road) consists of several benches elevated during post-glacial rebound.

 

Clints and grykes, typical karst structures, are well developed all over the Black Head platform, controlled by dominant fracture trends. They provide succor and shelter to a variety of small shrubs and wild flowers.

 

Smaller scale dissolution limestone rills are common along exposed gryke walls

 

Polished limestone along the Black Head shore reveal fossil corals and brachiopods. The stepped landforms are controlled by dominant fracture trends.

 

Tidal pools, regularly flushed by incoming tides.

 

Bouldery storm ridges have been pushed over the Black Head platform by Atlantic storms.

 

Typical vegetation eking out a living in the grykes. Succulents (left) are most common close to the shore.

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