Dr. Simon O'Toole
Submitted: Friday, 16th January 2009 by Mike Salway

Extra-solar planets are being discovered at an increasing rate and is one of the fastest growing fields in Astronomy. Dr Simon O'Toole, working at the Anglo-Australian Telescope is one of those at the forefront of this new research and is part of a team who has discovered more than 30 planets orbiting other stars.

Mike talks to Simon about his discoveries, the methods used to find extra-solar planets, and what the future holds in this exciting field. Will we find another Earth?


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Dr Simon O'Toole - planet hunter with the AAT

IIS: Let’s start with a bit about yourself. How old are you and where are you from?

SO'T: Age 32, grew up in Penrith, at the foot of the Blue Mountains in Sydney. Currently living in the Inner West of Sydney after spending three years in the south of Germany.

IIS: How and when did your interest in astronomy begin?

SO'T: It’s difficult to pin it down exactly. I always had an interest in space and astronomy, but only ever read about it growing up. We couldn’t afford a telescope when I was a kid. And I actually started studying to be an aerospace engineer, but became drawn to physics and then astronomy. If pushed I’d have to say that I decided to become an astronomer after I wrote a review paper in my 3rd year at university on the discovery of the first extra-solar planets.

IIS: Have you ever owned a telescope of your own?

SO'T: Sadly, no. But I hope to change this one day soon!

My research interests include extra-solar planets, especially detecting new ones...


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Anglo-Australian Observatory Dome. Photo Courtesy Barnaby Norris

IIS: What’s your current role at the AAO? What are you researching?

SO'T: I’m currently the Deputy Gemini Scientist as part of the Australian Gemini Office. Australia currently has a 6.2% share of the two 8m telescopes (in Hawaii and Chile). It’s 50% technical support and 50% research. My research interests include extra-solar planets, especially detecting new ones, stellar pulsation and white dwarfs.

IIS: Is it true that professional astronomers don’t actually get to look through an eyepiece? It must be a bit of a disappointment for amateurs to learn that professional astronomy is more about data gathering and analysis rather than time spent at the eyepiece of a big telescope.

SO'T: Sadly, this is true. That said, the old Mt Stromlo 74” (RIP) had a kind of eyepiece that I looked through as a student 10 years ago.

..We are now starting to actually image planets directly, which is very exciting!


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The Doppler method to measure a stars wobble

IIS: There are a number of techniques available to astronomers to search for extra-solar  planets. Can you briefly describe what they are and which method you use?

SO'T: Well, these days there are a growing number of methods. Until recently the successful ones were all indirect, i.e. we could only infer the existence of a planet, not see it directly. We are now starting to actually image planets directly, which is very exciting!

The indirect methods rely on measuring the gravitational tug of the planet on the star, the dimming of the star as the planet passes in front of it (or “transit”, similar to a solar eclipse or an occultation), or the amplification of a background star’s light by gravity (acting as a “lens”) as a host star and planet move across the line of sight to the background star.

The method we use with the Anglo-Australian Telescope relies on the gravitational tug of the star. We measure the Doppler shift of the star with incredibly high precision using spectroscopy. Think of a police siren: its pitch increases when it’s coming towards you and decrease when it’s moving away from you – that’s the Doppler effect. The same thing happens with light, only the light gets slightly bluer when something moves towards you and slightly redder when it moves away (that’s the “redshift”). The size of the shift gives you the mass of the planet, while the time it takes for one cycle gives you the orbital period. At the moment we can easily find planets like Jupiter and Saturn as they cause a large shift, while we cannot really find planets like Earth because they have tiny shifts. As our measurements become more precise though we are getting closer! The stars themselves cause problems as motions on the surface also cause Doppler shifts that can mimic planets – this is one of the areas of research I’m currently working on, how to minimise the “noise” from the stars.

IIS: How many planets around other stars have been discovered to-date? Which method has produced the most discoveries? How many has your team discovered?

SO'T: So far there have been 329 planets found, with seemingly more announced every week. Measuring the Doppler shift of stars has been the most successful, with probably around 250 planets found using this technique. At the AAT we’ve found 32 planets, so around 10% overall. The number of planets found using the “transit” method is increasing very quickly though, and will probably overtake the Doppler shift method before too long.

Combining these two methods gives you a lot more information about the planets than each method by itself. As I mentioned above, we are now imaging planets directly!

..the most important thing though is to go to space, as the Earth’s atmosphere causes too much distortion.


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The transit method to measure a stars brightness dip

IIS: Most of the planets that have been discovered so far are many times larger than the Earth, and orbit many times closer to their parent stars (“Hot Jupiters”). Is this simply a consequence of the methods we’re using to find them?

SO'T: Definitely! The Doppler shift method is very susceptible to large things close to their star – in fact it was first used to find binary stars. Another biasing effect is the simple fact that we’ve only been doing this for 10-12 years, so there are several planets with orbital periods similar to Jupiter (10 years or more) where we are only just starting to see complete orbits. The transit method is also more susceptible to close-in planets.

IIS: What technological or other advances are going to spur on the next round of discoveries of extra-solar planets that are more like Earth? More sensitive instruments? Larger telescopes? Space-based telescopes?

SO'T: A combination of all of these will be needed. Probably the most important thing though is to go to space, as the Earth’s atmosphere causes too much distortion. The Hubble Space Telescope could probably find Earth-like planets, but we cannot afford the time it would take to do so. The next space missions (in particular, one called Kepler) will stare at 100,000 stars for three or so years to search for the incredibly small dimming caused by an Earth-like planet “transiting” its star. Finding even one of these will be tremendously exciting! Larger telescopes in space with more sensitive instruments are the way to go!

...I think we will hear more about the definition of a planet in the future.

IIS: Will we find another “Earth” or an equivalent Solar System to our own?

SO'T: I’d say yes and it’s only a matter of time. There are too many stars out there for there to be nothing else like our Solar System out there. There are several space missions planned (especially Kepler, described above) that should find Earth-like planets. Also the next generation of ground-based telescopes with mirrors of 20-40m will be able to not only take pictures of other solar systems (which we can do already to a certain extent), but also investigate the planets’ atmospheres!

IIS: Have you had the opportunity to travel much in your job as an astronomer? Where’s the best place you’ve been?

SO'T: I’ve been lucky enough to do a fair bit of travelling, both for conferences and observations. I’ve been to plenty of conferences all over Europe and one in China. I’ve been to Chile to observe with the Very Large Telescope and hopefully next year will go to Hawaii to use Gemini. Probably the most amazing place I’ve been so far has been Cerro Paranal, home of the Very Large Telescope, where they have no measured rainfall in recorded history of over 400 years! The place is incredibly dry – so dry that they have to truck water in twice a day! I’ve been to Chile a few times now, and it’s a favourite spot, but my all time favourite would have to be a little town outside Brussels called Leuven. Beautiful town, wonderful people, plentiful beer… what more could you want on a nice summer’s day?

IIS: Is Pluto a Planet?

SO'T: Hahaha, no. At least not according to the official definition of a planet! But, in my opinion the definition is flawed. It has three parts: the object must orbit a star, but not be a star; be massive enough that gravity forces it to be almost spherical; and it must have cleared its neighbourhood of small bodies. Pluto is a “dwarf planet” which is basically defined by the first two criteria. My problem is that there are some objects out there that are approximately the same mass as Jupiter but do not orbit anything. What are these objects? Also, they are very vague about the last point – there are many Near Earth Asteroids out there, does this mean the Earth has not cleared its neighbourhood of small bodies? I think we will hear more about the definition of a planet in the future.

IIS: The amateur astronomy community is quite small in Australia - do you think that astronomy as a hobby will grow in the years to come?

SO'T: For sure – it all comes down to access. The price of a good-sized telescope is coming down, as is the price of a good digital camera. This has made astrophotography much more accessible than in the past.

IIS: Is light pollution killing the ability to do scientific astronomy for both amateurs and professionals? Are the observatories going to have to move further and further away to get the dark skies they need?

SO'T: Sadly, light pollution is becoming more and more of a problem for optical and infrared astronomers, especially for amateur astronomers. I remember my first visit to Siding Spring as a student being amazed that you could see the lights from Sydney. Also, the old Mt Stromlo Observatory was an excellent dark site when it was first conceived, but by the time it burnt down, Canberra had grown into a city of 300,000 people. That said, you can still do a lot not very far away from the city; it just depends what you want to do.

There are a few very dark sites with excellent conditions for professional observatories around the world: northern Chile and Hawaii are the two main ones, but La Palma in the Canary Islands is also very good. Sadly Australia does not really have any good sites. Siding Spring is relatively dark, but the seeing can be very variable.

Space is an (expensive) option, although you still have to worry about Earthshine and other scattered light. Thankfully you can minimise these effects – space telescopes use very sophisticated baffles and other devices to do this.

IIS: What motivates you? What inspires you? Both professionally and personally.

SO'T: Professionally, what motivates me is my love for astronomy. This can be the only thing that keeps me going at work sometimes – bureaucracy and politics can be very trying at times! Personally, I just love finding things out and learning new things. This of course means that I have a wealth of fascinating but ultimately useless knowledge!

IIS: Do you have any spare time? What do you enjoy doing when you’re not searching for another Earth?

SO'T: I do have some spare time; it’s not all work, work, work! I’m a bit of a football nut, so I spend as much as possible following the (currently not so) mighty Sydney FC. That can at times be rather painful though! I’m also a bit of an amateur psephologist… in other words I love following politics and in particular polling. Sad, I know!

IIS: What are the most influential books you’ve ever read?

SO'T: I’m not really sure if any books have really influenced me, but if pressed I’d have to say Carl Sagan’s Demon Haunted World and the ol’ classic Lord of the Rings by J. R. R. Tolkien. Special mention goes to Red Mars by Kim Stanley Robinson.

IIS: What are you reading right now?

SO'T: I’m slowly but surely getting through The Universe in a Mirror  by Robert Zimmerman, which is the story of the conception, design and construction of the Hubble Space Telescope. I’d be going faster if I had more time! It’s a fascinating account of the drama surrounding the most useful and exciting telescope in history.

IIS: What’s your favourite colour and what’s your favourite bit?

SO'T: I don’t really have a favourite colour, although I don’t mind blue. ? My favourite bit is the end.

IIS: Thankyou very much for taking the time to talk to IceInSpace.

References and Further Reading

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