Thursday, May 17, 2012

Infertility FAQ's: All that you want to know about infertility, its management and treatment

Infertility FAQ's

What is infertility?

Infertility means not being able to get pregnant after one year of trying. Or, six months, if a woman is 35 years of age or older. Women who can get pregnant but are unable to stay pregnant may also be infertile.

Pregnancy is the result of a process that has many steps. To get pregnant—

A woman’s body must release an egg from one of her ovaries (ovulation).
The egg must go through a fallopian tube toward the uterus (womb).
A man's sperm must join with (fertilize) the egg along the way.
The fertilized egg must attach to the inside of the uterus (implantation).

Infertility can happen if there are problems with any of these steps.

Is infertility a common problem?

Yes. About 10 % of women (6.1 million) in the United States ages 15–44 years have difficulty getting pregnant or staying pregnant.

Is infertility just a woman's problem?

No, infertility is not always a woman's problem. Both women and men can have problems that cause infertility. About one-third of infertility cases are caused by women’s problems. Another one third of fertility problems are due to the man. The other cases are caused by a mixture of male and female problems or by unknown problems.

What causes infertility in men?

Infertility in men is most often caused by—

A problem called varicocele (VAIR-ih-koh-seel). This happens when the veins on a man’s testicle(s) are too large. This heats the testicles. The heat can affect the number or shape of the sperm.
Other factors that cause a man to make too few sperm or none at all.
Movement of the sperm. This may be caused by the shape of the sperm. Sometimes injuries or other damage to the reproductive system block the sperm.

Sometimes a man is born with the problems that affect his sperm. Other times problems start later in life due to illness or injury. For example, cystic fibrosis often causes infertility in men.

What increases a man's risk of infertility?

A man's sperm can be changed by his overall health and lifestyle. Some things that may reduce the health or number of sperm include—

Heavy alcohol use
Drugs
Smoking cigarettes
Age
Environmental toxins, including pesticides and lead
Health problems such as mumps, serious conditions like kidney disease, or hormone problems
Medicines
Radiation treatment and chemotherapy for cancer

What causes infertility in women?

Most cases of female infertility are caused by problems with ovulation. Without ovulation, there are no eggs to be fertilized. Some signs that a woman is not ovulating normally include irregular or absent menstrual periods.

Ovulation problems are often caused by polycystic ovarian syndrome (PCOS). PCOS is a hormone imbalance problem which can interfere with normal ovulation. PCOS is the most common cause of female infertility. Primary ovarian insufficiency (POI) is another cause of ovulation problems. POI occurs when a woman’s ovaries stop working normally before she is 40. POI is not the same as early menopause.

Less common causes of fertility problems in women include—

Blocked fallopian tubes due to pelvic inflammatory disease , endometriosis , or surgery for an ectopic pregnancy
Physical problems with the uterus
Uterine fibroids , which are non-cancerous clumps of tissue and muscle on the walls of the uterus

What things increase a woman's risk of infertility?

Many things can change a woman's ability to have a baby. These include—

Age
Smoking
Excess alcohol use
Stress
Poor diet
Athletic training
Being overweight or underweight
Sexually transmitted infections (STIs)
Health problems that cause hormonal changes, such as polycystic ovarian syndrome andprimary ovarian insufficiency

How does age affect a woman's ability to have children?

Many women are waiting until their 30s and 40s to have children. In fact, about 20% of women in the United States now have their first child after age 35. So age is a growing cause of fertility problems. About one-third of couples in which the woman is older than 35 years have fertility problems.

Aging decreases a woman's chances of having a baby in the following ways—

Her ovaries become less able to release eggs
She has a smaller number of eggs left
Her eggs are not as healthy
She is more likely to have health conditions that can cause fertility problems
She is more likely to have a miscarriage

How long should women try to get pregnant before calling their doctors?

Most experts suggest at least one year. Women aged 35 years or older should see their doctors after six months of trying. A woman's chances of having a baby decrease rapidly every year after the age of 30.

Some health problems also increase the risk of infertility. So, women should talk to their doctors if they have—

Irregular periods or no menstrual periods
Very painful periods
Endometriosis
Pelvic inflammatory disease
More than one miscarriage

It is a good idea for any woman to talk to a doctor before trying to get pregnant. Doctors can help you get your body ready for a healthy baby. They can also answer questions on fertility and give tips on conceiving.

How will doctors find out if a woman and her partner have fertility problems?

Doctors will do an infertility checkup. This involves a physical exam. The doctor will also ask for both partners’ health and sexual histories. Sometimes this can find the problem. However, most of the time, the doctor will need to do more tests.

In men, doctors usually begin by testing the semen. They look at the number, shape, and movement of the sperm. Sometimes doctors also suggest testing the level of a man's hormones.

In women, the first step is to find out if she is ovulating each month. There are a few ways to do this. A woman can track her ovulation at home by—

Writing down changes in her morning body temperature for several months
Writing down how her cervical mucus looks for several months
Using a home ovulation test kit (available at drug or grocery stores)

Doctors can also check ovulation with blood tests. Or they can do an ultrasound

of the ovaries. If ovulation is normal, there are other fertility tests available.

Some common tests of fertility in women include—

Hysterosalpingography (HIS-tur-oh-sal-ping-GOGH-ru-fee): This is an X-ray of the uterus and fallopian tubes. Doctors inject a special dye into the uterus through the vagina. This dye shows up in the X-ray. Doctors can then watch to see if the dye moves freely through the uterus and fallopian tubes. This can help them find physical blocks that may be causing infertility. Blocks in the system can keep the egg from moving from the fallopian tube to the uterus. A block could also keep the sperm from reaching the egg.
Laparoscopy (lap-uh-ROS-kuh-pee): A minor surgery to see inside the abdomen. The doctor does this with a small tool with a light called a laparoscope (LAP-uh-roh-skohp). She or he makes a small cut in the lower abdomen and inserts the laparoscope. With the laparoscope, the doctor can check the ovaries, fallopian tubes, and uterus for disease and physical problems. Doctors can usually find scarring and endometriosis by laparoscopy.

Finding the cause of infertility can be a long and emotional process. It may take time to complete all the needed tests. So don't worry if the problem is not found right away.

How do doctors treat infertility?

Infertility can be treated with medicine, surgery, artificial insemination, or assisted reproductive technology. Many times these treatments are combined. In most cases infertility is treated with drugs or surgery.

Doctors recommend specific treatments for infertility based on—

Test results
How long the couple has been trying to get pregnant
The age of both the man and woman
The overall health of the partners
Preference of the partners

Doctors often treat infertility in men in the following ways—

Sexual problems: Doctors can help men deal with impotence or premature ejaculation. Behavioral therapy and/or medicines can be used in these cases.
Too few sperm: Sometimes surgery can correct the cause of the problem. In other cases, doctors surgically remove sperm directly from the male reproductive tract. Antibiotics can also be used to clear up infections affecting sperm count.
Sperm movement: Sometimes semen has no sperm because of a block in the man’s system. In some cases, surgery can correct the problem.

In women, some physical problems can also be corrected with surgery.

A number of fertility medicines are used to treat women with ovulation problems. It is important to talk with your doctor about the pros and cons of these medicines. You should understand the possible dangers, benefits, and side effects.

What medicines are used to treat infertility in women?

Some common medicines used to treat infertility in women include—

Clomiphene citrate (Clomid®): This medicine causes ovulation by acting on the pituitary gland. It is often used in women who have polycystic ovarian syndrome (PCOS) or other problems with ovulation. This medicine is taken by mouth.
Human menopausal gonadotropin or hMG (Repronex®, Pergonal®): This medicine is often used for women who don't ovulate due to problems with their pituitary gland—hMG acts directly on the ovaries to stimulate ovulation. It is an injected medicine.
Follicle-stimulating hormone or FSH (Gonal-F®, Follistim®): FSH works much like hMG. It causes the ovaries to begin the process of ovulation. These medicines are usually injected.
Gonadotropin-releasing hormone (Gn-RH) analog: These medicines are often used for women who don't ovulate regularly each month. Women who ovulate before the egg is ready can also use these medicines. Gn-RH analogs act on the pituitary gland to change when the body ovulates. These medicines are usually injected or given with a nasal spray.
Metformin (Glucophage®): Doctors use this medicine for women who have insulin resistance and/or PCOS . This drug helps lower the high levels of male hormones in women with these conditions. This helps the body to ovulate. Sometimes clomiphene citrate or FSH is combined with metformin. This medicine is usually taken by mouth.
Bromocriptine (Parlodel®): This medicine is used for women with ovulation problems due to high levels of prolactin. Prolactin is a hormone that causes milk production.

Many fertility drugs increase a woman's chance of having twins, triplets, or other multiples. Women who are pregnant with multiple fetuses have more problems during pregnancy. Multiple fetuses have a high risk of being born too early (prematurely). Premature babies are at a higher risk of health and developmental problems.

What is intrauterine insemination (IUI)?

Intrauterine insemination (IUI) is an infertility treatment that is often called artificial insemination. In this procedure, the woman is injected with specially prepared sperm. Sometimes the woman is also treated with medicines that stimulate ovulation before IUI.

IUI is often used to treat—

Mild male factor infertility
Women who have problems with their cervical mucus
Couples with unexplained infertility

What is assisted reproductive technology (ART)?

Assisted reproductive technology (ART) is a group of different methods used to help infertile couples. ART works by removing eggs from a woman's body. The eggs are then mixed with sperm to make embryos. The embryos are then put back in the woman's body.

How often is assisted reproductive technology (ART) successful?

Success rates vary and depend on many factors. Some things that affect the success rate of ART include—

Age of the partners
Reason for infertility
Clinic
Type of ART
If the egg is fresh or frozen
If the embryo is fresh or frozen

CDC collects success rates on ART for some fertility clinics. According to the CDC’s 2010 Preliminary ART Success Rates, the average percentage of ART cycles that led to a live birth were—

42% in women younger than 35 years of age
32% in women aged 35–37 years
22% in women aged 38–40 years
12% in women aged 41–42 years
5% in women aged 43–44 years

ART can be expensive and time-consuming. But it has allowed many couples to have children that otherwise would not have been conceived. The most common complication of ART is multiple fetuses. But this is a problem that can be prevented or minimized in several different ways.

What are the different types of assisted reproductive technology (ART)?

Common methods of ART include—

In vitro fertilization (IVF) means fertilization outside of the body. IVF is the most effective ART. It is often used when a woman's fallopian tubes are blocked or when a man produces too few sperm. Doctors treat the woman with a drug that causes the ovaries to produce multiple eggs. Once mature, the eggs are removed from the woman. They are put in a dish in the lab along with the man's sperm for fertilization. After 3 to 5 days, healthy embryos are implanted in the woman's uterus.
Zygote intrafallopian transfer (ZIFT) or Tubal Embryo Transfer is similar to IVF. Fertilization occurs in the laboratory. Then the very young embryo is transferred to the fallopian tube instead of the uterus.
Gamete intrafallopian transfer (GIFT) involves transferring eggs and sperm into the woman's fallopian tube. So fertilization occurs in the woman's body. Few practices offer GIFT as an option.
Intracytoplasmic sperm injection (ICSI) is often used for couples in which there are serious problems with the sperm. Sometimes it is also used for older couples or for those with failed IVF attempts. In ICSI, a single sperm is injected into a mature egg. Then the embryo is transferred to the uterus or fallopian tube.

ART procedures sometimes involve the use of donor eggs (eggs from another woman), donor sperm, or previously frozen embryos. Donor eggs are sometimes used for women who can not produce eggs. Also, donor eggs or donor sperm is sometimes used when the woman or man has a genetic disease that can be passed on to the baby. An infertile woman or couple may also use donor embryos. These are embryos that were either created by couples in infertility treatment or were created from donor sperm and donor eggs. The donated embryo is transferred to the uterus. The child will not be genetically related to either parent.

Surrogacy

Women with no eggs or unhealthy eggs might also want to consider surrogacy. A surrogate is a woman who agrees to become pregnant using the man's sperm and her own egg. The child will be genetically related to the surrogate and the male partner. After birth, the surrogate will give up the baby for adoption by the parents.

Gestational Carrier

Women with ovaries but no uterus may be able to use a gestational carrier. This may also be an option for women who shouldn't become pregnant because of a serious health problem. In this case, a woman uses her own egg. It is fertilized by the man's sperm and the embryo is placed inside the carrier's uterus. The carrier will not be related to the baby and gives him or her to the parents at birth.

Recent research by the Centers for Disease Control showed that ART babies are two to four times more likely to have certain kinds of birth defects. These may include heart and digestive system problems, and cleft (divided into two pieces) lips or palate. Researchers don’t know why this happens. The birth defects may not be due to the technology. Other factors, like the age of the parents, may be involved. More research is needed. The risk is relatively low, but parents should consider this when making the decision to use ART.

All About Scabies - III : How to prevent and control scabies

Prevention & Control of Scabies

When a person is infested with scabies mites the first time, symptoms may not appear for up to two months after being infested. However, an infested person can transmit scabies, even if they do not have symptoms. Scabies usually is passed by direct, prolonged skin-to-skin contact with an infested person. However, a person with crusted (Norwegian) scabies can spread the infestation by brief skin-to-skin contact or by exposure to bedding, clothing, or even furniture that he/she has used.

Scabies is prevented by avoiding direct skin-to-skin contact with an infested person or with items such as clothing or bedding used by an infested person. Scabies treatment usually is recommended for members of the same household, particularly for those who have had prolonged skin-to-skin contact. All household members and other potentially exposed persons should be treated at the same time as the infested person to prevent possible reexposure and reinfestation. Bedding and clothing worn or used next to the skin anytime during the 3 days before treatment should be machine washed and dried using the hot water and hot dryer cycles or be dry-cleaned. Items that cannot be dry-cleaned or laundered can be disinfested by storing in a closed plastic bag for several days to a week. Scabies mites generally do not survive more than 2 to 3 days away from human skin. Children and adults usually can return to child care, school, or work the day after treatment.

Persons with crusted (Norwegian) scabies and their close contacts, including household members, should be treated rapidly and aggressively to avoid outbreaks. Institutional outbreaks can be difficult to control and require a rapid, aggressive, and sustained response.

Rooms used by a patient with crusted scabies should be thoroughly cleaned and vacuumed after use. Environmental disinfestation using pesticide sprays or fogs generally is unnecessary and is discouraged.

All About Scabies - II : Diagnosis, symptoms and complications

Diagnosis of Scabies

Diagnosis of a scabies infestation usually is made based upon the customary appearance and distribution of the the rash and the presence of burrows.

Whenever possible, the diagnosis of scabies should be confirmed by identifying the mite or mite eggs or fecal matter (scybala). This can be done by carefully removing the mite from the end of its burrow using the tip of a needle or by obtaining a skin scraping to examine under a microscope for mites, eggs, or mite fecal matter (scybala). However, a person can still be infested even if mites, eggs, or fecal matter cannot be found; fewer then 10-15 mites may be present on an infested person who is otherwise healthy.

Symptoms

When a person is infested with scabies mites the first time, symptoms usually do not appear for up to two months (2-6 weeks) after being infested; however, an infested person still can spread scabies during this time even though he/she does not have symptoms.

If a person has had scabies before, symptoms appear much sooner (1-4 days) after exposure. An infested person can transmit scabies, even if they do not have symptoms, until they are successfully treated and the mites and eggs are destroyed.

Common Symptoms

The most common symptoms of scabies, itching and a skin rash, are caused by sensitization (a type of “allergic” reaction) to the proteins and feces of the parasite. Severe itching (pruritus), especially at night, is the earliest and most common symptom of scabies. A pimple-like (papular) itchy (pruritic) “scabies rash” is also common. Itching and rash may affect much of the body or be limited to common sites such as:

between the fingers,
wrist,
elbow,
armpit,
penis,
nipple,
waist,
buttocks,
shoulder blades.

The head, face, neck, palms, and soles often are involved in infants and very young children, but usually not adults and older children.

Tiny burrows sometimes are seen on the skin; these are caused by the female scabies mite tunneling just beneath the surface of the skin. These burrows appear as tiny raised and crooked (serpiginous) grayish-white or skin-colored lines on the skin surface. Because mites are often few in number (only 10-15 mites per person), these burrows may be difficult to find. They are found most often in the webbing between the fingers, in the skin folds on the wrist, elbow, or knee, and on the penis, breast, or shoulder blades.

Possible Complications

The intense itching of scabies leads to scratching that can lead to skin sores. The sores sometimes become infected with bacteria on the skin, such as Staphylococcus aureus or beta-hemolytic streptococci. Sometimes the bacterial skin infection can lead an inflammation of the kidneys called post-streptococcal glomerulonephritis.

Crusted (Norwegian) scabies

Crusted (Norwegian) scabies is a severe form of scabies that can affect the elderly, persons who are immunocompromised, or persons who have conditions that prevent them from itching and/or scratching (spinal cord injury, paralysis, loss of sensation, mental debility). Crusted scabies is characterized by vesicles and thick crusts over the skin that can contain many mites. Itching (pruritus) may be absent in crusted scabies because of a patient’s altered immune status or neurological condition. Because they are infested with large numbers of mites (up to 2 million), persons with crusted scabies are very contagious. Persons with crusted scabies may not show the usual signs and symptoms of scabies such as the characteristic rash or itching (pruritus).

All About Scabies - I : How Scabies is Transmitted

Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The microscopic scabies mite burrows into the upper layer of the skin where it lives and lays its eggs. The most common symptoms of scabies are intense itching and a pimple-like skin rash. The scabies mite usually is spread by direct, prolonged, skin-to-skin contact with a person who has scabies.

Scabies occurs worldwide and affects people of all races and social classes. Scabies can spread rapidly under crowded conditions where close body contact is frequent. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks.

How Scabies is Transmitted

Human scabies is caused by an infestation of the skin by the human itch mite (Sarcoptes scabiei var. hominis). The adult female scabies mites burrow into the upper layer of the skin (epidermis) where they live and deposit their eggs. The microscopic scabies mite almost always is passed by direct, prolonged, skin-to-skin contact with a person who already is infested. An infested person can spread scabies even if he or she has no symptoms. Humans are the source of infestation; animals do not spread human scabies.

Persons at Risk

Scabies can be passed easily by an infested person to his or her household members and sexual partners. Scabies in adults frequently is sexually acquired.

Scabies is a common condition found worldwide; it affects people of all races and social classes. Scabies can spread easily under crowded conditions where close body and skin contact is common. Institutions such as nursing homes, extended-care facilities, and prisons are often sites of scabies outbreaks. Child care facilities also are a common site of scabies infestations.

Crusted Scabies

Some immunocompromised, elderly, disabled, or debilitated persons are at risk for a severe form of scabies called crusted, or Norwegian, scabies. Persons with crusted scabies have thick crusts of skin that contain large numbers of scabies mites and eggs. The mites in crusted (Norwegian) scabies are not more virulent than in non-crusted scabies; however, they are much more numerous (up to 2 million per patient). Because they are infested with such large numbers of mites, persons with crusted (Norwegian) scabies are very contagious to other persons. In addition to spreading scabies through brief direct skin-to-skin contact, persons with crusted scabies can transmit scabies indirectly by shedding mites that contaminate items such as their clothing, bedding, and furniture. Persons with crusted scabies should receive quick and aggressive medical treatment for their infestation to prevent outbreaks of scabies.

World Health Organisation: New data highlight increases in hypertension, diabetes incidence

The World health statistics 2012 report puts the spotlight on the growing problem of the noncommunicable diseases burden.

One in three adults worldwide, according to the report, has raised blood pressure – a condition that causes around half of all deaths from stroke and heart disease. One in 10 adults has diabetes.

“This report is further evidence of the dramatic increase in the conditions that trigger heart disease and other chronic illnesses, particularly in low- and middle-income countries,” says Dr Margaret Chan, Director-General of WHO. “In some African countries, as much as half the adult population has high blood pressure.”

For the first time, the World Health Organization’s annual statistics report includes information from 194 countries on the percentage of men and women with raised blood pressure and blood glucose levels.

In high-income countries, widespread diagnosis and treatment with low-cost medication have significantly reduced mean blood pressure across populations – and this has contributed to a reduction in deaths from heart disease. In Africa, however, more than 40% (and up to 50%) of adults in many countries are estimated to have high blood pressure. Most of these people remain undiagnosed, although many of these cases could be treated with low-cost medications, which would significantly reduce the risk of death and disability from heart disease and stroke.

Also included for the first time in the World health statistics 2012 are data on people with raised blood glucose levels. While the global average prevalence is around 10%, up to one third of populations in some Pacific Island countries have this condition. Left untreated, diabetes can lead to cardiovascular disease, blindness and kidney failure.

Obesity another major issue

“In every region of the world, obesity doubled between 1980 and 2008,” says Dr Ties Boerma, Director of the Department of Health Statistics and Information Systems at WHO. “Today, half a billion people (12% of the world’s population) are considered obese.”

The highest obesity levels are in the WHO Region of the Americas (26% of adults) and the lowest in the WHO South-East Asia Region (3% obese). In all parts of the world, women are more likely to be obese than men, and thus at greater risk of diabetes, cardiovascular disease and some cancers.

Noncommunicable diseases currently cause almost two thirds of all deaths worldwide. Global concern about the rise in numbers of deaths from heart and lung disease, diabetes and cancer prompted the United Nations to hold a high-level meeting on noncommunicable diseases in New York in September 2011.

The World Health Assembly, to be held in Geneva from 21 to 26 May 2012, will review progress made since that meeting and agree on next steps. Work is currently under way to develop a global monitoring framework and a set of voluntary targets for prevention and control of these diseases.

Published annually by WHO, the World health statistics is the most comprehensive publication of health-related global statistics available. It contains data from 194 countries on a range of mortality, disease and health system indicators including life expectancy, illnesses and deaths from a range of diseases, health services and treatments, financial investment in health, as well as risk factors and behaviours that affect health.

Some key trends in this year’s report are:

Maternal mortality: In 20 years, the number of maternal deaths has decreased from more than 540 000 deaths in 1990 to less than 290 000 in 2010 – a decline of 47%. One third of these maternal deaths occur in just two countries – India with 20% of the global total and Nigeria with 14%.
10 year trends for causes of child death: Data from the years 2000 to 2010 show how public health advancements have helped save children’s lives in the past decade. The world has made significant progress, having reduced the number of child deaths from almost 10 million children aged less than 5 years in 2000 to 7.6 million annual deaths in 2010. Declines in numbers of deaths from diarrhoeal disease and measles have been particularly striking.
Death registration: Only 34 countries (representing 15% of the world’s population) produce high-quality cause-of-death data. In low and middle-income countries, less than 10% of deaths are registered.

NASA finds a new count of potentially hazardous asteroids

Observations from NASA's Wide-field Infrared Survey Explorer (WISE) have led to the best assessment yet of our solar system's population of potentially hazardous asteroids. Also known as "PHAs," these asteroids have orbits that come within five million miles (about eight million kilometers) of Earth, and they are big enough to survive passing through Earth's atmosphere and cause damage on a regional, or greater, scale.

The asteroid-hunting portion of the WISE mission, called NEOWISE, sampled 107 PHAs to make predictions about the population as a whole. Findings indicate there are roughly 4,700 PHAs, plus or minus 1,500, with diameters larger than 330 feet (about 100 meters). So far, an estimated 20 to 30 percent of these objects have been found.

In this simulated view of the near-Earth asteroid population, potentially hazardous asteroids (PHAs) are denoted in orange. Less dangerous near-Earth asteroids are blue. Earth's orbit is green.

While previous estimates of PHAs predicted similar numbers, they were rough approximations. NEOWISE has generated a more credible estimate of the objects' total numbers and sizes. Because the WISE space telescope detected the infrared light, or heat, of asteroids, it was able to pick up both light and dark objects, resulting in a more representative look at the entire population.

"The NEOWISE analysis shows us we've made a good start at finding those objects that truly represent an impact hazard to Earth," said Lindley Johnson, program executive for the Near-Earth Object Observation Program at NASA Headquarters. "But we've many more to find, and it will take a concerted effort during the next couple of decades to find all of them that could do serious damage or be a mission destination in the future."

This orbit diagram illustrates the difference between a PHA and less hazardous near-Earth asteroids (NEA).

The new analysis suggests that about twice as many PHAs as previously thought reside in low-inclination orbits, which are roughly aligned with the plane of Earth's orbit.

"Our team was surprised to find the overabundance of low-inclination PHAs," said Amy Mainzer, NEOWISE principal investigator, at NASA's Jet Propulsion Laboratory. "Because they will tend to make more close approaches to Earth, these targets can provide the best opportunities for the next generation of human and robotic exploration."

The NEOWISE analysis suggests a possible origin for the low-inclinaton PHAs: Many of them could have originated from a collision between two asteroids in the main belt lying between Mars and Jupiter. A larger body with a low-inclination orbit may have broken up in the main belt, causing some of the fragments to drift into orbits closer to Earth and eventually become PHAs.

The lower-inclination PHAs appear to be somewhat brighter and smaller than other near-Earth asteroids. The discovery that PHAs tend to be bright says something about their composition; they are more likely to be either stony, like granite, or metallic. This type of information is important in assessing the space rocks' potential hazards to Earth. The composition of the bodies would affect how quickly they might burn up in our atmosphere if an encounter were to take place.

"The NEOWISE project, which wasn't originally planned as part of WISE, has turned out to be a huge bonus," said Mainzer. "Everything we can learn about these objects helps us understand their origins and fate."

The Earth and the Worlds beyond

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Thursday, May 17, 2012