Putting Exoplanets on the Scale

Astronomers have come up with a new technique for measuring an alien planet’s mass, and therefore its composition and potential habitability, even when standard methods don’t work.

You’d never ask a woman her weight. (Actually, you’d never ask a man either.) But for exoplanets, the answer is crucial.

Hot Jupiter

De Wit and Seager (both MIT) have found a new way to measure exoplanets’ mass. For now, the technique is largely only useful for hot Jupiters, but future telescopes will allow them to scale the technique to nearby Earth-sized planets.
C. Carreau / ESA / Nature

Knowing the mass of an alien planet, along with its radius, tells astronomers whether the exoplanet is rocky, watery, or gaseous. In modeling, the mass can even influence whether the planet could host magnetic fields or plate tectonics. In the December 20th Science, Julien de Wit and MacArthur Fellow Sara Seager (both MIT) have found a forward-thinking technique to measure the all-important number.

To measure the mass of an alien planet dozens or hundreds of light-years away, astronomers usually watch for the star’s wiggle in response to the planetary tug. The wiggle comes from the fact that planets don’t actually orbit their parent stars — the star and planet orbit a mutual center of mass. So as the planet orbits, the star orbits too, albeit in a much smaller circle. (The mutual center can be inside the star itself, even if not at the core.)

Stellar wobble is easiest to see when massive planets orbit close to their parent stars, such as with hot Jupiters. But the punier the planet and the farther it orbits, the more weakly the star wobbles. And even if we could measure a star’s slowest sway, which we can’t yet (current telescopes can only measure a star’s velocity down to about 1 mile per hour), starspots and other activity on the star’s surface might cover up a planet-induced signal. That’s the case for hot Jupiter WASP-33, whose parent star pulsates strongly.

A New Way to Weigh Exoplanets

With some creative thinking, de Wit and Seager have found a new way to weigh an exoplanet: by watching it transit across the face of its parent star. When a planet transits, starlight passes through the thin sliver of its outer atmosphere. This passage imprints the starlight with the chemical fingerprints of the atmosphere’s composition. Astronomers collect thistransmission spectrum during transit observations, measuring which wavelengths pass through the atmosphere and which are absorbed.

Transiting exoplanet

When an exoplanet transits across the face of its parent star, starlight passes through a thin sliver of its atmosphere. De Wit and Seager show how measuring the atmosphere’s extent can give the planet’s mass.
NASA Goddard Space Flight Center

De Wit and Seager determined that, because a more massive planet can collect a thicker gaseous shroud around itself, using these transmission spectra to measure the atmosphere’s extent could in theory also reveal the planet’s mass.

It’s not a clear-cut connection: the atmosphere’s extent also depends on its temperature (heat comes from the parent star and the planet itself) and the weight of its molecules. A hot Jupiter will have light molecules in its atmosphere, mostly hydrogen and helium. But a rocky planet’s atmosphere will be composed of heavier stuff such as oxygen, carbon dioxide, and nitrogen. De Wit and Seager show that they can calculate each of these parameters directly from the same transmission spectrum.

This isn’t just a theoretical exercise: the astronomers used the well-studied hot Jupiter HD 189733b to prove the technique works. Radial velocity had already shown the planet has a mass between 1.1 and 1.2 Jupiters; de Wit and Seager’s transmission spectroscopy calculations gave a mass of 1.15 Jupiters.

“This [technique] appears to be very promising,” says exoplanetary scientist Jonathan Fortney (University of California, Santa Cruz). “I think that in practice clouds will confound the technique a bit more than they suggest, but I think it will work a lot of the time.”

Scaling Down

TESS satellite

The TESS satellite will monitor bright, nearby stars for transiting exoplanets. Though its focus is Sun-like stars, it will also catch some 10,000 M dwarfs in its view.
TESS team

For now, hot Jupiters remain the main target for the new technique. Their puffy, extended atmospheres make them good targets for transmission spectroscopy. But de Wit and Seager aim to describe super-Earths and Earth-size planets. Current telescopes can’t take transmission spectra of these smaller words, but the upcoming James Webb Space Telescope could. Scheduled for launch in 2018, it will be able to weigh Earth-size planets orbiting the coolest M dwarf stars up to about 160 light-years away. Its reach will extend twice that far for super-Earths.

Unfortunately, that meansKepler’s 167 confirmed exoplanets and 3,500 candidates will be largely out of reach.

“You wouldn’t be able to do this for stars in the Kepler field, which are too far away and faint,” Fortney explains. “But Kepler wasn’t designed to find planets around bright stars that would be amenable to atmospheric characterization.” Instead a number of upcoming projects, including SPECULOOS and TESS (launching in 2017), will focus on finding planets orbiting nearby stars, whose atmospheres will be easier to study.

The ultimate goal. says de Wit, is to combine all the available data for an exoplanet — including both the wobble of its star and the extent of its atmosphere — to better estimate its mass and understand its atmosphere . The more tools in astronomers’ toolbox, the better, because it’s not enough to just count exoplanets anymore, it’s time to see what they’re made of.

Extract from Sky & Telescope Magazine December 2013

Cosmology & Theology – start here?

Recently I came across this short essay which asks some the key questions on the debate between cosmology and theology. More can be found on Diarmuid O’Murchu’s website.



From Universe to Multiverse

(READER’s NOTE: Officially, the word multiverse means several universes existing simultaneously. It is sometimes used to refer to the possibility that other universes existed before the present one, and others may succeed it. I use the term with BOTH meanings in mind).

Galileo was hammered by the Catholic Church for endorsing the Copernican theory  that the Earth revolved around the Sun, putting the Sun and not the Earth at the centre of the Milky Way galaxy. We were awakening to a new expansive view of the universe, although it would take almost another 400 years before we would break the firm grip of ecclesiastical control and scientific reductionism. In 1650, the noted Biblical scholar, Archbishop James Ussher calculated that the creation of the world took place on Oct. 23rd, 4004 BCE, and that the end of the world would occur at noon on Oct 23rd., 1997. That became standard Catechetical teaching in many parts of the Christian world up to about 1960.

Meanwhile, a mind-shift had happened in the early 1900s with Einstein’s theories of Relativity and the formulation of the Quantum Theory. It was no longer the Earth that engaged the searching mind but the universe at large, now so complex and mysterious that talk about its beginning or end seemed short-sighted and even irrelevant. 

Towards the Big Bang

With the Hubble discoveries of the late 1920s and the pioneering work of the Belgian priest-astronomer, Georges Lemaitre, the seeds were sown for the leading theory of 20th. Century science: The Big Bang. The term was coined by Fred Hoyle in the 1940s but only became a formal theory after the discovery of the cosmic background radiation by Arno Penzias and Robert Wilson in 1963. From a single point of energy, 13-15 billion years ago, everything we know in creation today began to unfold, including Planet Earth which first evolved about 4.0 billion years ago.

That which gave us the evidence for the Big Bang threw up other imponderables, particularly the discovery of powerful gravity in the distant horizons of time-space. The strength of the gravity waves suggests that great quantities of matter exist out there somewhere. Its nature and location we know nothing about as yet, but scientists are forced to the bewildering conclusion that the observable world comprises at most 10% of the known universe, which means we know nothing about 90% of the created universe.

It has taken discoveries of this nature to challenge the arrogance with which we humans study and propose theorise about the created universe. The real issue of course is neither discovery nor study, but POWER. We feel we have the right to be in control, absolute control and this is still the driving force behind a great deal of modern science, and sadly behind a good deal of religious dogmatism as well.

Another Quantum Leap ?

Finally we come to the real big stuff: the multiverse. The story can be traced back to 1957 when an American doctoral student, Hugh Everett (supervised by the Princeton professor, John A. Wheeler), proposed the possible existence of several rather than one universe. His argument is based on mathematical equations derived from Quantum Theory which also leads to the notion that the universe is self-creating and poised for indefinite growth and expansion.

In the 1981, the idea of a multiverse got an added boost from Alan Guth’s inflationary theory. Quantum theory postulates the existence of an original empty space (hence, the quantum vacuum), consisting of energy movements (fluctuations) from which all matter is shaped and formed. Guth proposes that the fluctuations initially manifest like bubbles in a foam, and shortly after the big bang, these bubbles expanded (inflated) each becoming a mini-universe in its own right. A great deal of experimental evidence supports this proposal. And it is strongly endorsed by leading scientists of our time including Andri Linde (Moscow & Stanford), Marin Rees (Cambridge), Brian Green (Columbia), Paul Davies (Sydney).

I find the adoption of fractal geometry particularly inspiring: “Recent versions of inflationary theory assert that instead of being a ball of fire, the universe is a huge growing fractal.” (Andrei Linde). Fractals are revolutionary new mathematical image-like concepts, in which we find repeated patterns buried deeper and deeper (a bit like a Russian doll). The more we unravel the observable pattern (through computer simulations) the more we find it repeated in the subsistent layers. It is a wonderful exposition of the leading principle of the new physics: the whole is greater than the sum of the parts, yet the whole is contained in each part. (for more on fractals see my book, Quantum Theology, 2004, pp.51-53).

Theological Implications.

For those who wish to delve deeper, the web pages I cite at the end will provide additional information on these complex ideas. How do we relate these discoveries to the realm of faith, Christian or otherwise? I offer a few thoughts.

1. Long before religion ever evolved, humans believed that the divine was intimately involved in creation. All the religions support this idea. Is creation then a kind of primary revelation of God to us? If so, we need to attend carefully to how we understand creation.

2. Our human tendency especially in the past 2000 years is to reduce creation to a human artefact, one we can use and subdue to our advantage; all the major religions, to one degree or another, endorse this orientation. Consequently, we can no longer assume that the religious understandings of creation are in any way adequate – spiritually or theologically.

3. Although scientists also embrace the addictive preoccupation with power and control, many of their intuitions into cosmic and planetary life may be much more spiritually informed than the insights of formalised religions. On the other hand, several of these scientific insights are congruent with those of great mystics from all the religious traditions of humankind.

4. Christian theologians exhibit strong concern about the notion of creatio ex nihilo (creation from nothing). They wish to retain this belief in order to safeguard divine initiative, and presumably their understanding of divine power. Today, we understand the primordial nothingness as a substratum of seething creativity. Perhaps, for God, the notion of a beginning-point is of no significance. Might it not be another anthropocentric fascination!

5. Scriptures of all traditions allude to the end of the world. It is very explicit in the
Christian and Muslim traditions. Contemporary science is rapidly moving towards the notion of a world without beginning or end. Might this not be a stronger indicator of truth, rather than the anti-world stance that underpins some of the major religions?

6. The big fear – scientifically and religiously – generated by many of these new ideas  concerns our human place and role in the plan of creation. It is abundantly clear that we are not in charge, that we are not the ultimate species in any sense, that we rely on many other aspects of creation to survive on earth, that we are one small organism among so many others, and disturbingly, not as wise as we would like to think. So what is our purpose? Of all the responses to this question the one I find most challenging and inspiring is the proposal that we are creation becoming aware of itself. Our unique vocation – and contribution to creation – is to enhance the growth in consciousness. An awesome responsibility! (Perhaps, this is what all the great mystics were, and are, about!)

7. Theologically, the crucial issue is around the notion of revelation. If the divine has been disclosing creativity and meaning in the entire story of creation, throughout these billions of years, why restrict the empowerment of the divine to religiously-validated time and culture boundaries? Somehow, it does not seem to make sense anymore!

Useful Source material:

For a useful overview of current thinking on the Multiverse, see: George Ellis, “Does the Multiverse Really Exist?” Scientific American, Vol 305 (Aug 2011), 18-23.
John Gribbin (2009), In Search of the Multiverse.
Joel Primack & Nancy Abrams (2006)The View from the Center of the Universe.

WEB Pages:
http://www.edge.org: edited by John Brockman,engages leading scientists in ongoing dialogue.