Friday, October 24, 2014

Astronomy can help develop poor countries

Why should a developing nation such as Brazil invest in Astronomy while there is still poverty in the country? Because Astronomy is key to fight poverty and improve lives.

Countries that invest less in science have more human poverty. Figure by Jorge Meléndez based on

Astronomy is THE interdisciplinary science per excellence. It is based on physics and maths, but it can also involve other areas such as chemistry, meteorology, geology, biology, history and archeology; it has also a strong technological component, as advanced technology is required to built large telescopes and state-of-the-art instrumentation. Astronomy can greatly contribute to improve education at different levels, helping students to interconnect apparently unrelated areas. More importantly, Astronomy fascinate children, being thus an excellent vehicle for introducing them to science and technology, which are fundamental to develop a country.

Soccer is a national passion in Brazil, where soccer players are celebrities. It is OK to follow soccer as a career, but certainly a country needs other role models besides soccer players. We urgently need inspiring role models in science, we need successful scientists performing cutting-edge science. If we aspire to make major discoveries, we certainly need appropriate facilities. Brazilian astronomers were very excited back in 2010, when Brazil signed an agreement to join ESO, the largest and more productive observatory on Earth; unfortunately, Brazilian authorities are taking too long to ratify it.

The Southern sky as seen from Brazil. (c) Babak Tafreshi
An example of how astronomical discoveries can promote science in Brazil, was the oldest solar twin identified by an international team led by Brazilian astronomers in 2013. An important implication is that it helped to solve the lithium mystery in the Sun. The news was highlighted both internationally and nationally, with more than 100 local media reporting the discovery. A local competition made to "name" the oldest solar twin, received almost one thousand entries, showing thus an important impact. Other recent exciting finding by Brazilian astronomers was the discovery of rings around an asteroid, known previously only around giant planets. Another example by a developing country is the recent successful Indian space mission to Mars, showing how great science achievements can be a matter of national pride.

Brazil's exports are mainly primary mineral and agricultural products. We need more than just exporting coffee and bananas to develop a country. The development of technology in Brazil is way behind other countries; most high tech products are either imported or just assembled here. We need to invest heavily in education, science and technology, and Astronomy can help to educate our children, and stimulate our most talented minds to follow careers in science and technology.

Sunday, October 19, 2014

New simulations explain why Mars is so small

Press release IAG/2014-02, Embargoed until 2014 February 20 at 13:00 UT

Press-release example by Viviana Peña Márquez, student of Divulgação em Astronomia at IAG/USP

Astronomers present model to help solve Mars’ size mystery 

Existent planet formation theories have successfully explained why there are jovian and terrestrial planets in our solar system, but have failed to justify why the Red Planet is so small. According to most models, Mars should be as big as Venus and Earth, but the planet is only a tenth of its neighbours  Through new simulations, an international team led by Brazilian astronomer André Izidoro, shed light on the mystery of why Mars failed to grow similar in size.

Previous simulations of planet formation, with a solar nebula that varies smoothly with distance from the Sun, produce a body with approximately the size of our own planet Earth in the orbit of Mars, i.e. 1.5 AU* from the Sun. A puzzling matter since the four rocky planets are composed by the same planetary embryos.

Following studies showed that a planet with the size of Mars could have formed in its orbit if the solar nebula was nonuniform, with a belt containing more material near today’s Earth, followed by a belt with less material in the region where the Red Planet is today.

Contrast between “Grand Tack” model (B) and Izidoro’s model (A). (c) Science

Up to now, the most valid theory to explain such unusual distribution is called the “Grand Tack” model, that assumes the inward and then outward migration of Jupiter. These unlikely events in the early Solar System could have created favorable conditions for the formation of a planet such as Mars.

Looking for a better alternative to the “Grand Tack” model, Izidoro and his team assumed that material flowed toward the Sun moving at different speeds at different distances from the star, generating a depletion of material somewhere between 1 AU and 3 AU. A gap that could explain Mars’ size. “This deficit in local mass may be common in protoplanetary disks. However, the location and characteristics of this region can be very sensitive to the properties of each model. In our case, Mars formation around 1.5 AU is also due to the gravitational effects exerted by Jupiter and Saturn,” explains Izidoro. 

Othon Winter, researcher of the UNESP Orbital Dynamics and Planetology Group, concludes: “The model is quite complete because, besides giving an explanation to the mystery of the size of the Red Planet, it also maintains and manages to generate the other terrestrial planets in their current orbits and masses.”

This research was presented in the paper “Terrestrial planet formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars”, by André Izidoro et al. to appear in the Astrophysical Journal Letters (February 2014).

The team is composed of André Izidoro (Universidade Estadual Paulista, Brazil [UNESP] - University of Nice-Sofia, France), Nader Haghighipour (University of Hawaii-Manoa, USA), Othon Winter (UNESP), and Masayoshi Tsuchida (UNESP). 


Research Paper


* One astronomical unit (AU) is the distance from the Earth to the Sun.

André Izidoro
University of Nice-Sophia, Nice, France.
Phone: xx x xxxx xxxx
E-mail: xxxxxxx@xxxxx.xxxx.xx

Wednesday, October 15, 2014

From the Peruvian Andes to galaxies and the Big Bang

A century ago our universe was just a little village called the Milky Way. Today, we know that there are billions of galaxies in the cosmos, and that the universe is expanding due to the Big Bang. The Peruvian Andes played a fundamental role in those discoveries.

Less than a century ago, Edwin Hubble showed that certain "nebulae" are actually galaxies like our Milky Way, by using the so-called period-luminosity relationship of variable stars known as cepheids, that allowed him to estimate distances. Using cepheids located in the Andromeda "nebula", Hubble concluded in the 1920s that Andromeda is far outside our Galaxy. Later, Hubble found that the most distant galaxies have the largest velocities away from Earth. This means that the Universe is expanding, and that everything started in the Big Bang.

Andromeda "nebula". (c) NASA.
Hubble relied on the period-luminosity relationship of cepheids to estimate how far away are distant galaxies. This relationship was discovered by American astronomer Henrietta Leavitt, using observations taken in the Peruvian Andes, more exactly from the Boyden Station in Arequipa. The Harvard College Observatory built that observatory in the 1890s and early 1900s, to have access to the Souther Sky. Henrietta Leavitt measured the brightness of variable stars in the Magellanic Clouds, and discovered the period-luminosity relationship followed by cepheid variables.

Thus, observations from the Peruvian Andes were key to set the standard ruler to measure large distances, leading to the birth of Extragalactic Astronomy and Cosmology. In another post I'll describe how observations gathered in Harvard's observatory in Arequipa led to the birth of Stellar Astrophysics.

Sunday, October 12, 2014

Stellar populations. I) What is the difference between population and sample?

How many stars are in the Milky Way? The total population of stars in our Galaxy is enormous (about a few hundred billion). We cannot count or study every single star in our Galaxy, hence Astronomers must select relatively small samples of stars (hundreds or thousands) to study our Galaxy.

Milky Way as seen from Paranal. (c) ESO
How to select a sample that is representative of a large population? This is far from trivial; incorrect conclusions can be obtained if there is a bias in the selection. An example is the study of the mean age of the whole population of stars in our Galaxy. Imagine that to do this job you select a sample of stars located in the Galactic halo, far away from the Galactic disk. Halo stars are old (about 10 Gyr), therefore you would incorrectly conclude that stars in our Galaxy are mostly old.

Problems with sample selection can also affect our daily life. Think about polls for a Presidential election, like the one we're having in Brazil. Poll companies cannot interview the population of all Brazilian voters, they have to select a sample that is not necessarily representative of the entire population. Indeed, the results of the first round were surprising, candidate Aécio Neves was the runner-up, gathering far more votes than those estimated from the polls. He will face current President Dilma in a second round, on October 26, 2014.

Monday, October 6, 2014

18 Sco, a solar twin rich in "technological" heavy elements

If there are hypothetical planets around the solar twin 18 Sco, they should be rich in heavy elements such as silver, neodymium, dysprosium and europium. Here on Earth, many of those heavy elements are like "gold", because they are precious ingredients for some electronics. If there are habitable planets around 18 Sco, their civilisations will not lack these precious elements important in today's technology. 18 Sco is also rich in refractory elements, that are elements that in the early solar system easily formed dust, later planetesimals, and finally larger rocky objects such as Earth. Technical details on how the chemical abundances were obtained are given in Meléndez et al. (2014).

What is a solar twin?

Depending on how stars resemble the Sun, astronomers refer to them as "solar type" stars, "solar analogs" and "solar twins". Solar twins are the the most similar to the Sun.

A solar type star actually belongs to a broad category. Back in the XIX century, Father Angelo Secchi (1868, Sugli Spettri Prismatici Delle Stelle Fisse) observed bright stars using a spectrograph (an instrument that splits the light with such a power than besides the colours we can see lines from different chemical elements) and found that yellow stars showed a spectrum similar to the Sun's, hence called them tipo solare. The similarity was due to the limitations of early spectrographs. Work performed later divided those yellow stars actually in 3 different types, F, G (like the Sun) and K stars (see more about Stellar classification here), More specifically, solar type stars include stars from late F (the coolest F stars), G (like our Sun) and early K (the hottest K stars).

A solar analog is more similar to the Sun, yet with important variations, such as differences in temperatures of up to 250 degrees in relation to the Sun, and with a chemical composition within a factor of 2 - 3 of the Sun's.

Solar twins are stars nearly identical to the Sun in all their properties (such as mass, temperature, chemical composition). For example, it has been suggested that solar twins should have temperatures within 100 degrees and chemical composition within 25% of the Sun (Ramírez 2009). The first star recognised as a solar twin was 18 Sco. This is the brightest solar twin, yet it is barely visible to the naked eye. The star that most approaches the concept of solar twin is HIP 56948, also known as Intipa Awachan. Since stars of the same mass and chemical composition evolve in the same way, astronomers also call solar twins those stars with about the Sun's mass and composition. Hence, solar twins evolve as the Sun. Solar twins of different ages gives us the fascinating possibility of studying the past and future of the Sun. The oldest known solar twin is HIP 102152.